OBJECTIVE: To quantify the relation between weight change and change in blood pressure, lipids and insulin levels, and determine if this relation differs by race or initial level of obesity. DESIGN: Longitudinal cohort study. SETTING AND PARTICIPANTS: Community-based sample of 3325 black and white men and women aged 18-30 y from four centers followed for 10 y. Women pregnant at baseline or 10th year exam and persons without a recorded weight at both exams were excluded. Participants whose baseline BMI was ≥25 kg/m2 were classified as overweight. Height, weight, HDL-cholesterol (HDL-C), LDL-cholesterol (LDL-C), fasting triglycerides, fasting insulin, and blood pressure were measured at baseline and Year 10. RESULTS: The mean (s.d.) of weight gained over 10 y was 10.5 (10.0) kg (black men), 11.7 (11.0) (black women), 7.7 (8.0) (white men), and 7.2 (10.0) (white women). An increase in weight was associated with adverse changes in all factors in all race-sex groups. For example, a 9.1 kg (20-lb) weight increase in persons not overweight at baseline predicted an increase in LDL-C ranging from 0.23 mmol/l in black women to 0.28 mmol/l in black men and a decrease in HDL-C from 0.09 mmol/l (white women) to 0.11 mmol/l (white men) (all P<0.0001). The estimated change in triglycerides was greater in white than in black participants (P<0.02); no other racial differences were found. Changes in triglycerides (P<0.00001) and fasting insulin (P=0.004) were greater in men than in women. Only for LDL-C was a weight change-associated increase significantly different (greater, P<0.001) for nonoverweight persons than for those overweight at baseline. None of these associations were highly specific. Mean levels of LDL-C, HDL-C, and systolic blood pressure improved among all those who lost or did not gain weight. CONCLUSIONS: A 10 y weight gain in young adults of both races and sexes tends to confer adverse changes in their levels of LDL-C, HDL-C, triglycerides, fasting insulin, and blood pressure. This effect occurs regardless of initial weight, age, race, or gender.