Our aim is to investigate visfatin concentration and its relationship to glycated hemoglobin (HbA1c), insulin resistance, lipid parameters, and neonatal birth weight in women with gestational diabetes mellitus (GDM). In our study group, there were 47 women with GDM and 31 women with normal glucose tolerance (NGT) between 33-39 weeks of gestation. Plasma visfatin levels were significantly decreased in pregnant women with GDM compared to those with NGT (p=0.001). Homeostasis model assessment-insulin resistance (HOMA-IR) levels were higher in the GDM group than in the NGT group (p=0.006). In all subjects, plasma visfatin levels were negatively correlated with HOMA-IR, post-prandial blood glucose, triglycerides, and VLDL cholesterol (p<0.05). We did not observe any statistically significant correlation between the plasma visfatin levels and the selected parameters in the GDM group, but in the NGT group plasma visfatin levels were negatively correlated with HOMA-IR (r=-0.36, p=0.04). There was no correlation between visfatin concentrations and fetal birth weight in either group (p>0.05). By regression analysis, having GDM was found to be the only significant determinant (t=3.5, p=0.001) of visfatin concentration (R=0.39, r2=0.15). We conclude that women with GDM have significantly decreased visfatin concentrations in the third trimester. Future studies are required to establish the exact role of visfatin in the pathogenesis of GDM. ©2008, Editrice Kurtis.