Studies of delayed conception and risk of gestational diabetes (GDM) are sparse, although common underlying mechanisms are plausible, including insulin resistance and inflammation. The association between a history of infertility and GDM was assessed prospectively among 40,773 eligible pregnancies in the US Nurses' Health Study II cohort (1989-2001). Biennial questionnaires provided updated information on infertility and several lifestyle and health-related characteristics. Multivariable log-binomial models with generalized estimating equations were used to compute risk ratios and 95% confidence intervals, adjusting for age, prepregnancy body mass index (weight (kg)/height (m)(2)), and additional potential confounders. GDM occurred among 1,405 (5.2%) women. A prepregnancy history of infertility was reported by 5,497 (20.5%) participants and was significantly associated with a 39% greater risk of GDM (risk ratio (RR) = 1.39, 95% confidence interval (CI): 1.24, 1.57; P < 0.001). Underlying reasons for infertility associated with GDM included ovulation disorders (RR = 1.52, 95% CI: 1.23, 1.87; P < 0.001) and tubal blockage (RR = 1.83, 95% CI: 1.20, 2.77; P = 0.005). The association of cervical mucus disorder with GDM was of borderline significance (RR = 1.70, 95% CI: 0.88, 3.30; P = 0.11). Endometriosis (RR = 1.27, 95% CI: 0.70, 2.31; P = 0.43) and male factor infertility (RR = 1.12, 95% CI: 0.78, 1.61; P = 0.55) were not associated with GDM risk. These novel findings suggest that infertility, particularly from ovulation disorders and tubal blockage, is associated with an increased GDM risk. Further research is needed to identify mechanisms or common underlying metabolic dysfunction explaining these observations.