We prospectively evaluated fasting serum total cholesterol (chol), low- and high-density lipoprotein cholesterol (LDL-chol and HDL-chol), and triglycerides (TGs) in a large cohort of Hispanic women during the first 36 mo after pregnancies complicated by gestational diabetes mellitus (GDM). In 1340 women studied 6-12 wk postpartum (PP-GDM group), chol and LDL-chol were similar to levels in 43 postpartum control subjects without prior GDM. Compared with control subjects (2.01 +/- 1.24 mM), TG was elevated in the PP-GDM women with diabetes mellitus (DM) (2.86 +/- 2.21 mM, P less than 10(-5)) and impaired glucose tolerance (IGT) (2.64 +/- 1.68 mM, P = 0.02) but not in those with normal glucose tolerance (2.00 +/- 1.21 mM). HDL-chol was decreased in PP-GDM women with DM compared with those with normal glucose tolerance. A subgroup of 157 women with prior GDM returned for at least one annual follow-up test on nonhormonal contraception (FU-GDM: n = 60 at 3-11 mo after delivery, n = 78 at 12-23 mo, and n = 39 at 24-35 mo). The cumulative prevalence of DM by 36 mo was 40%. Chol or LDL-chol levels did not significantly change during the 1-yr intervals in the FU-GDM group and were similar to a control group of 36 women without prior GDM. TG was elevated and HDL-chol was decreased in the FU-GDM women with DM at 3-11 mo but not thereafter. Overall, the prevalence of moderate- and high-risk LDL-chol in the FU-GDM group was not different from that of control subjects. These findings suggest that lipid abnormalities are uncommon during the first 36 mo after delivery in women with recent GDM. The abnormalities found consisted of increased TG and decreased HDL-chol in subjects who had developed DM during the study period.