BACKGROUND & AIMS:Gestational diabetes mellitus (GDM) prevalence is increasing worldwide. To the best of our knowledge the specific evaluation of soft drink consumption as a risk factor for developing GDM has only been conducted in the Nurses' Health Study II. OBJECTIVE:To investigate the incidence of GDM according to soft drink consumption in the SUN project. DESIGN:The "Seguimiento Universidad de Navarra" (SUN) project is a prospective and dynamic cohort which included data of 3396 women who notified at least one pregnancy between December 1999 and March 2012. A validated 136-item semi-quantitative food frequency questionnaire was used to assess soft drink consumption. Four categories of sugar-sweetened soft drink (SSSD) and diet soft drink (DSD) consumption (servings) were established: rarely or never (<1/month), low (1-3/month), intermediate (>3/month and ≤1/week) and high (≥2/week). Potential confounders were adjusted through non-conditional logistic regression models. RESULTS:During the follow-up, we identified 172 incident cases of GDM. After adjusting for age, baseline body mass index, family history of diabetes, smoking, total energy intake, physical activity, parity, fast-food consumption, adherence to Mediterranean dietary pattern, alcohol intake, multiple pregnancy, cardiovascular disease/hypertension at baseline, fiber intake, following special diet and snacking, SSSD consumption was significantly associated with an increased risk of incident GDM, with multivariable adjusted odds ratios (OR) of 2.03 (95% confidence interval [CI]: 1.25-3.31) and 1.67 (95% CI: 1.01-2.77) for the highest and intermediate categories, respectively, versus the lowest category (p for linear trend: 0.006). Conversely, DSD consumption was not associated with GDM incidence (adjusted OR: 0.82; 95% CI: 0.52-1.31) for the highest versus the lowest category (p for linear trend: 0.258). Additional sensitivity analyses did not change the results. CONCLUSION:Higher consumption of SSSDs before pregnancy was an independent risk factor for GDM, however, no association was observed between DSD consumption and GDM risk.