Objective : The purposes of this study were to determine the prevalence of gestational diabetes mellitus (GDM) in Trabzon city of Turkey and to identify appropriate risk factors for gestational diabetes in pregnant mothers. Research design and methods : Eight hundred and seven adult pregnant women were screened for GDM with a 1-hour, 50 g oral glucose challenge test (GCT). Three-hour, 100 g oral glucose tolerance tests (GTTs) were performed on screen-positive women. Results : Of the 807 pregnancies screened, 59 (7.3%) had an initial oral GCT result of greater than or equal to140 mg/dl. Diagnostic testing with the oral GTT was performed on the 59 screen-positive gravid women. Of those tested, 10 were diagnosed with GDM on the basis of greater P criteria over 3 hours, for a prevalence of 1.23%. Significant associations were found between age, body mass index (BMI) and GDM positivity (p < 0.01 and p < 0.05; respectively). The prevalence of GDM was associated with diastolic blood pressure (DBP) and weeks gestation (p < 0.05). There was no significant association between increased BMI, systolic blood pressure, number of pregnancies and GDM positivity. In addition, the birth weights of the babies born to mothers with GDM were significantly higher than those of the non-diabetic healthy mothers babies (p < 0.001). Conclusions : The prevalence of GDM in a Turkish population was low. The prevalence of GDM showed an increase with the ages of pregnant women, gestational age and DBP. This study demonstrates that the universal screening for GDM is not mandatory in our pregnant population. The cost of universal screening may be prohibitive in our population. Large prospective studies are needed to better analyze outcome data and efficacy of screening in adult pregnancies.