Too old for the annual pediatrician visit - and too young for the annual mammogram or prostate exam - people in their 20s and 30s can easily go years without seeing a doctor. And sometimes, doctors say, that's OK.

"As long as men are feeling good, their weight is stable, they have no undue pain, they're functioning well at their job, in their relationships and at home, then for the most part, they don't need to be seen," said Dr. Ted Epperly, board chairman of the American Academy of Family Physicians. Same goes for young women, though they should have regular gynecological appointments for Pap smears and breast exams.

That doesn't mean young people are home-free. If you're having symptoms of anything - worst headache ever, bleeding from somewhere, pain in your chest, pain that lasts for longer than normal or impairs your ability to function -- you should be seen by a doctor, Epperly said.

HEALTH ISSUES TO KEEP AN EYE ON

Alcohol: Men should have no more than two drinks per day, and women should have no more than one per day, Epperly said. Alcohol causes damage to your liver, stomach and pancreas.

Depression: Young adulthood is a critical period for identifying mental health problems, which usually manifest by age 24. Depression is the most common problem, affecting 11 percent of young women and 6 percent of young men.

Hypertension & cholesterol: Three percent of young adults have hypertension (high blood pressure). The earlier you start treating it, the better chance of avoiding long-term problems such as heart attack, stroke and blindness, Epperly said. All adults older than 20 should get a cholesterol test every five years, says the National Cholesterol Education Program.

Obesity: If you are 30 pounds over your ideal weight, you are approaching obesity, Epperly said. To calculate your ideal weight: For men, give yourself 106 pounds for five feet of height, then add six pounds for every inch over five feet. For women, give yourself 100 pounds for five feet of height, then add five pounds for every inch over five feet. (This is a rough approximation; different body frames have different ideal weights).

Physical activity: Two-thirds of young adults don't get leisure physical activity. You should exercise at least 30 minutes per day, five days a week, Epperly said.

Sexually transmitted infections: Chlamydia, gonorrhea and HPV (human papillomavirus) peak during young adulthood, with 45 percent of women ages 20 to 24 testing positive for HPV. Both men and women should get tested for STIs if they're having unprotected sex. The CDC recommends girls and women under 26 get the HPV vaccineThe CDC this month stated that males age 9 to 26 "may" also get the HPV vaccine to guard against genital warts.

Vaccines: In addition to an annual flu vaccine, adults are supposed to get tetanus and diptheria vaccine every 10 years, and a whooping cough vaccine once between the ages of 18 and 65.

Cancer: Healthy lifestyle choices during young adulthood -- including good nutrition, quitting smoking and cutting back on alcohol -- are key to reducing the risk of cancer later in life, said Holly Trandel, cancer risk reduction program coordinator for the Robert H. Lurie Comprehensive Cancer Center at Northwestern University.

KEEP AN EYE OUT FOR THESE CANCERS

Testicular cancer: The most common cancer in men ages 15 to 35. See a doctor if there's pain, lumps or other testicular changes, Trandel said.

Skin cancer: Be alert to new or changing skin growths, and see a doctor if you notice moles that have the A-B-C-D characteristics: Asymmetrical, Border irregularity, Color and Diameter. (It could be bad if it's bigger than the size of a pencil eraser.)

Cervical cancer: It is caused by HPV but is preventable. Starting no later than age 21, women should get a pelvic exam and Pap smear annually.

Breast cancer: Women in their 20s and 30s should have a clinical breast exam every three years, Trandel said. Mammograms are recommended to start at 40, but if you have a family history of breast cancer, talk to your doctor about earlier screenings. Generally, be aware of what your breasts look and feel like and report any changes to your doctor.