Summary Aim: Resistin is believed to play a certain role in the pathogenesis of gestational diabetes mellitus (GDM). The aim of the study was to assess resistin concentrations in women with diet-treated GDM and good glycemic control, in healthy pregnant women and in cord blood, depending on the advancement of the pregnancy, maternal body mass index (BMI) and index of insulin resistance (HOMA-IR), as well as on somatic features of the newborns. Materials and Methods: The study group consisted of 20 women with GDM whereas 20 healthy women constituting the control group. They were examined twice: at 23-32 weeks and at 35-37 weeks of gestation. Serum resistin concentration was assessed using RIA method. Results: In the control group, maternal resistin concentration was higher (p<0,03) after the second examination than the first one. In the GDM group, maternal resistin concentration was similar to that in the control group in both examinations. No correlations were found either between maternal resistin and insulin concentrations or between maternal resistin concentration and BMI or HOMA-IR. No correlations were found between maternal resistin concentration or cord blood resistin concentration and somatic features of newborns, either. In both groups, resistin concentration in cord blood was higher than in maternal blood during both examinations. Conclusions: Our results indicate that maternal resistin concentration increases as pregnancy advances. In women with diet-treated GDM and good glycemic control resistin concentration is similar to that observed in healthy pregnant women. No relationship was found between resistin concentration in cord blood and somatic features of the newborns.