When the Guidells of Pasadena go on vacation, they don't worry about ever feeling lonely. They have friends Brad and Dawn and Frank and Maureen, one set of grandparents and two other families to keep them company.

"It's second nature to us to plan one big trip," says Nicholas Guidell, 25, whose vacation to a Myrtle Beach, S.C., campground last week included 30 travelers altogether. "You get to experience different things with people you know."

From the beaches to the mountains, the family vacation is showing signs of turning into something bigger -- the multifamily vacation. No longer is the summer trip about Mom, Dad and the kids. Now, it could just as easily be about cousins, neighbors, friends from college, and your kids' best friends sharing a get-away.

At Sun Realty on North Carolina's Outer Banks, multifamily homes are the fastest growing segment of the rental market. Six, seven and even eight bedroom homes, often with several master bedrooms, are not uncommon.

"This is a trend we've been seeing for years," says Melanie Buchanan, a Sun manager.

It's much the same at Smuggler's Notch resort in northern Vermont, where group vacations -- from family reunions to a bunch of friends from the office -- will often lease two or more neighboring hillside condominiums for a ski vacation.

"We have some larger condominiums with two master bedrooms that just lend themselves to two families at a time," says Barbara Thomke, a spokeswoman for the resort. "It's not unusual for people to make new friends here -- when you find a place you enjoy you're likely to find people you enjoy, too -- and come back to be with them."

One group leading the trend is grandparents who may vacation with several generations of family. Just in the past year, the percentage of grandparents who traveled with grandchildren rose more than 20 percent from the year before, according to a recent poll by Yesawich, Pepperdine & Brown, an Orlando, Fla., travel consultant.

But baby boomers are in the thick of it, too. So are single parents who want the comfort and convenience of traveling with other families.

"We're seeing more and more of this. People in their 30s and 40s who have grown up together and now have children and go off together on vacation," says Lynda Maxwell, owner of Destinations Inc., an Ellicott City travel agency. "This is often how they get to see each other once a year. It's a good way to stay in touch."

The advantages are obvious -- more time for family or friends to be together in a pleasant surrounding, sharing expenses (and babysitters) and chores (like cooking and laundry) -- not to mention a lot more camaraderie and greater opportunity to socialize.

"It's a wonderful experience," says Oliver Link, 68, a Carrolton, Ga., retired college professor who rents a Nags Head, N.C., house for himself, two sons, a daughter-in-law's brother and his wife, his brother and his wife and a family friend. "It's better than Christmas gatherings. No hustle and bustle, just pure relaxation."

Avoiding conflicts

Learning how to organize such a vacation -- and keep potential conflicts and even generational differences at bay -- is not as easy as it sounds. People who get along fine in small doses aren't always ready for a week or two together.

Two years ago, travel writer Christine Loomis flew from her home in Boulder, Colo., to France with two female friends and their children. Trouble brewed when issues of discipline arose -- who could say (or yell) what to which youngsters. She hasn't traveled with them since.

"We were all great friends," says Loomis, author of Family Travel: How to Plan a Family Vacation The Whole Family Can Enjoy (Reader's Digest, 1998). "You have to think about these things in advance."

Veteran group vacationers agree that advance planning may be the most critical step -- figuring out finances, schedules, and accommodations in advance. After all, who wants to find out you're sleeping on a sofa at the last moment?

The Guidells have been traveling with friends from their Glen Burnie church for 12 years -- going on camping trips as often as monthly and in groups as large as 50. For each destination, one of a dozen or so families is assigned to organize the trip and handle reservations and other details. On the next trip, a different family will take over.

"It probably took six to eight trips for us to figure out the system," says Larry Guidell, 52, who accompanied his son Nicholas to Myrtle Beach.

Paul Macala of Southington, Conn., has taken multifamily vacationing to new heights. He sends out weekly newsletters regarding his annual ski vacation in September. That's five months before the four-day trip.

But he practically has to. What started out as a group of 38 friends and co-workers at a local hospital has turned into a annual pilgrimage for 250.

"The more information you can give people, the better. I send out maps, condo layouts, lists of local restaurants, everything," says Macala, 54, a carpenter. "When you do the work months and months in advance, you can just have fun when you get there. It's all about attention to detail."

The second most important step may be to give everyone a little space. There will be group activities, but there has to be some privacy, too, and time for people to do things on their own.

When the Guidells go camping, the individual families tend to go off on their own for most of the day, often choosing a younger person's activity (hiking or swimming), while the older vacationers adopt a more leisurely pace (antiquing or visiting historic sites). In the evening, the full group gets together around a campfire.

"You can always sightsee if you want to but you don't have to," says Rebecca Igoe of Glen Burnie, a longtime member.

Chores can sometimes be an issue, but experienced family travelers say potential conflicts can be avoided when everyone shares the load. Cooking dinner, cleaning up the dishes, taking out the trash and other duties are often rotated.

When Preston Modlin, an elementary school principal from Buena Vista, Va., vacationed at a beach house in Duck, N.C., last month, he knew that he and his wife would be cooking just one night in seven. They made tacos and fajitas for the group of 16, then enjoyed the pizza, ribs, shrimp, grilled fish and other dinners their fellow travelers prepared later that week.

Managing chores

"When we divide up chores, we make a point to make sure Mom doesn't clean up the kitchen on the last day," says Modlin, 42. "She'll want to save that quarter-jar of mayonnaise. We detour her so we can throw everything out."

Some chores are just a matter of looking out for yourself. While in Duck, all the children had to be sure to keep public areas clean, hang up wet towels and throw their bathing suits in the laundry. Breakfast and lunches were also strictly self-serve.

"As great as your friends or siblings or whomever may be, chances are you're not used to be around them 24 / 7," says Loomis, "and they can get on your nerves."

Seemingly minor details can turn into major headaches. For most people, vacation time is too precious to waste feuding over who failed to return the milk to the refrigerator or used the last of the laundry fabric softener.

"Going with [extended] family looks like the safest thing," says Linda Freeman, 38, an Elkridge police officer who recently shared a Nags Head beach house with seven relatives. "My dad always taught us to pick up after ourselves."

Nor is everyone necessarily cut out for group travel. It may require more flexibility than some people can muster. Yet for the Guidells and their friends, it's an appealing formula -- rarely does a newcomer try it and not like it.

"You should do it," says Igoe, who's been vacationing with the group for more than a decade. "It's like an extended family. If something goes wrong, you have people there for you. The close-knitness of things, you have someone to share with. We just love it."

How to keep the campers happy

Eager to try a multifamily vacation for the first time? Experienced travelers offer these tips to avoid the common pitfalls:

* Make your reservations early. Larger vacation rental homes are among the most popular properties these days.

* Don't have one person front all the deposit money. Unless Grandpa has decided to treat, it's better to share -- that way the group isn't left holding the bag for a last-minute no-show.

* Plan in advance and share information. Everyone needs to know what they're facing -- even what they should pack.

* Look for discounts. Big groups have some clout -- be sure to investigate discounts offered to groups and family reunions on cruises and resorts.

* Be loose. Don't plot every activity. Make certain everyone has to set his or her own schedule.

* Figure out finances first. Are you going to split every bill or break up expenses in some other way? Decide upfront and be sure everyone agrees.

* Plan parenting. One of the chief advantages of group travel is sharing the parenting load -- just don't stick it to one or two adults.

* Take it easy. Hey, you're on vacation. So what if your kids are staying up a little later or dinner was fast-food? Go with the flow, and you'll run into fewer conflicts.

-- Peter Jensen