OBJECTIVE: To investigate the association between a history of gestational diabetes mellitus (GDM) and overactive bladder (OAB) in women of premenopausal age. DESIGN: Population-based study. SETTING: The Swedish Twin Register. POPULATION: In 2005, a total of 14 094 female twins born between 1959 and 1985 in the Swedish Twin Registry participated in a comprehensive survey on common exposures and complex diseases. Structured questions provided information on GDM and OAB. The present study was designed as a cross-sectional analysis including all women in the cohort having given birth before 2005 (n = 7855). METHODS: A logistic regression model based on generalised estimating equations was used to derive odds ratios (ORs). MAIN OUTCOME MEASURE: The association between a history of GDM and OAB was estimated using ORs with 95% confidence intervals (CIs). RESULTS: The prevalence of OAB in women with a history of GDM was 19.1% compared with 10.7% in women without GDM. This corresponded to a two-fold increased odds of OAB in women with a history of gestational diabetes (OR 2.13, 95% CI 1.48–3.05). After adjusting the analysis for age, body mass index, parity, smoking, and diabetes mellitus, having had GDM was associated with doubled odds of OAB (OR 1.88, 95% CI 1.26–2.80). CONCLUSIONS: A history of GDM was positively associated with OAB among women of premenopausal age. The association does not seem to be mediated by body mass index or type-I or type-II diabetes mellitus.