Objective: To establish the risk of the gestational diabetes mellitus (GDM) with respect to maternal age and body mass index (BMI). Methods: The data of the patients, admitted to our clinic for pregnancy follow up between 2007 and 2011were collected retrospectively. 50 gram and 100 gram screening test results, birth weight of the newborns and demographic features of the patients were recorded. Results: 544 patients were included. Mean age of the patients was 30.2±4.2 years, mean BMI value was 23.3±4.1 kg/m2 (15.6-66), mean gestational age at delivery was 38.9±1.2 weeks (34.9-42), and mean birth weight was 3409±415 grams. The odds ratio for GDM at the patients above 40 years old was 7.84 and the odds ratio for patients with a body mass index ≥25 was 1.74. Conclusion: Gestational diabetes mellitus increases with advanced maternal age and body mass index. The patients with a body mass index ≥25 at the antenatal visits may be offered regular nutrition and exercise program and get pregnant after having a body mass index below 25 if possible.