Objective. - To examine the longitudinal associations between a pregnancy and persistent changes in adiposity in young black and white women. Design. - Prospective cohort study with 5 years of follow-up. Setting. - Participants recruited by community-based sampling (Birmingham, Ala; Chicago, Ill; and Minneapolis, Minn) and through the membership of a large prepaid health care plan (Oakland, Calif). Participants. - A total of 2788 women (53% black) aged 18 through 30 years were assessed at baseline (1985 through 1986) and reassessed at examination 2 (91% retention; 1987 through 1988) and examination 3 (86% retention; 1990 through 1991). Women who remained nulliparous (n=925) during the 5-year follow-up were compared with women who had a single pregnancy of 28 weeks' duration during that period and who were at least 12 months postpartum at follow-up (primiparas, n=89; multiparas, n=114). Main Outcome Measures. - Change in body weight and in waist-to-hip ratio during the 5-year period. Analyses were adjusted for demographic factors (age and education), behavioral variables (smoking and physical activity), and baseline level of adiposity. Results. - Primiparas within both race groups gained 2 to 3 kg more weight during the 5-year period than did nulliparas in both adjusted and unadjusted analyses. Primiparas also had greater increases in waist-to-hip ratio that were independent of weight gain. Multiparas did not differ from nulliparas in adiposity change in either race group. At each level of parity, black women demonstrated greater adverse changes in adiposity than did white women. Conclusions. - These data suggest that women experience modest but adverse increases in body weight and fat distribution after a first pregnancy and that these changes are persistent.