The aim of this study was to evaluate the association between fast food consumption and gestational diabetes mellitus (GDM) among Tehranian women. This study was conducted over a 17-month period, on a random sample of pregnant women ( = 1026), aged 18-45 years, attending prenatal clinics in five hospitals affiliated with universities of medical sciences, located in different districts of Tehran, Iran. Dietary data were collected during gestational age ≤6 weeks, using a 168-item valid and reliable food frequency questionnaire. Consumption of total fast foods including hamburgers, sausages, bologna (beef), pizza and French fries was calculated. Between 24 and 28 weeks of gestation, all pregnant women underwent a scheduled 100 g 3 h oral glucose tolerance test. GDM was defined according to the American Diabetes Association definition. The mean age and pre-pregnancy body mass index BMI of participants were 26.7 ± 4.3 years and 25.4 ± 4.5 Kg/m², respectively. A total of 71 women developed GDM. After adjustment for confounders, the OR (95% CI) for GDM for total fast food consumption was 2.12 (1.12-5.43) and for French fries it was 2.18 (1.05-4.70). No significant association was found between hamburgers, sausages, bologna (beef), pizza and GDM. Fast food consumption in women of reproductive age was found to have undesirable effects in the prevalence of GDM.