Objective: To determine whether gestational diabetes mellitus (GDM) is an independent risk factor for postpartum urinary incontinence in singleton pregnancies., Design: A longitudinal cohort study., Setting: A single tertiary-care hospital in Taiwan., Population: Pregnant women with term deliveries between 2002 and 2007 (n = 6653) were consecutively recruited., Methods: Logistic regression models were fitted based on generalised estimating equation methods to derive odds ratios for occurrences of type-specific urinary incontinence in the third trimester and at four time-points over 2 years during the postpartum period., Main Outcome Measures: Evaluation of whether GDM is an independent risk factor for postpartum urinary incontinence., Results: The full model analysis revealed that GDM was an independent risk factor for all type-specific urinary incontinence (odds ratio [95% confidence interval]: 1.97 [1.56-2.51], 3.11 [2.18-4.43] and 2.73 [1.70-4.40] for stress, urge and mixed incontinence, respectively]. Compared with women without GDM, women with GDM tended to exhibit more severe symptoms of stress incontinence for up to 2 years postpartum, whereas for urge or mixed incontinence, more severe symptoms were found only for 6 months postpartum. Evaluation of quality of life using the Incontinence Impact Questionnaire 7 suggested that women with GDM requiring insulin treatment had a higher likelihood of functional impairment than women with GDM requiring conservative treatment only or women without GDM (P < 0.05, by the chi-square test for trend)., Conclusions: GDM was found to be an independent risk factor for postpartum urinary incontinence and had a significant impact on quality of life. Women with GDM should be provided with timely consultation and support once urinary incontinence occurs., (© 2012 The Authors BJOG An International Journal of Obstetrics and Gynaecology © 2012 RCOG.)