We undertook this study to determine the incidence of diabetes mellitus (DM) and impaired glucose tolerance (IGT) after gestational diabetes mellitus (GDM). It is a follow-up study of a consecutive sample of women with GDM in a tertiary care center in Trinidad, West Indies. The cohort was a consecutive sample of 157 women with GDM who delivered in the hospital between June 1981 and December 1984. Of these, a volunteer sample of 60 women (38%) consented to participate 3.5–6.5 yr later. The two groups were remarkably similar in ethnic composition, mean age at index delivery, marital status, and family history of DM. Interviews revealed that 26 women (43%) had already developed DM for which they were receiving treatment. The remaining 34 women (57%) were given a 2-h 75-g oral glucose tolerance test, and fasting and half-hourly venous blood samples were obtained and analyzed for plasma glucose. Based on accepted diagnostic criteria, 11 (32%) of 34 had DM, 10 (29%) had IGT, and 13 (38%) had normal glucose tolerance. A total of 37 (62%) of 60 women had developed DM, and another 10 (17%) had IGT in the intervening 3.5–6.5 yr. The results support findings that GDM is associated with an increased risk of mothers developing DM in later life.