Self-report is often used in identifying gestational diabetes events in epidemiologic studies; however, validity data are limited, with little to no data on self-reported severity or treatment. We aimed to assess the validity of self-reported gestational diabetes diagnosis and evaluate the accuracy of glucose diagnosis results and gestational diabetes treatment self-reported at 6-week postpartum. Data were from 82 and 83 women with and without gestational diabetes, respectively, within the prospective National Institute Child Health and Human Development Fetal Growth Studies-Singletons (2009-2013). Medical record data were considered the gold standard. Sensitivity was 95% (95% confidence interval [CI] = 88, 98), and specificity was 100% (95% CI = 96, 100); four women with gestational diabetes incorrectly reported not having the disease, and none of the women without gestational diabetes reported having gestational diabetes. Sensitivity did not vary substantially across maternal characteristics including race/ethnicity. For women who attempted to recall their values (84/159 women), self-reported glucose challenge test results did not differ from the medical records (median difference: 0; interquartile range: 0-0 mg/dl). Medical records indicated that 42 (54%) of 78 women with confirmed gestational diabetes were treated by diet only and 33 (42%) were treated by medication. All 42 women with diet-treated gestational diabetes correctly reported having had diet and lifestyle modification, and 28 (85%) of 33 women with medication-treated gestational diabetes indicated postpartum that they had medication treatment. At 6-week postpartum, regardless of race/ethnicity or socioeconomic status, women accurately recalled whether they had gestational diabetes and, as applicable, their treatment method.