Objective: To evaluate the influence of gestational diabetes mellitus on weight discrepancy in twin pregnancies. Methods: 200 twin pregnancies were included in the study. 157 nondiabetic pregnant women with twin gestations and 43 twin pregnancies with gestational diabetes mellitus (GDM) with viable fetuses born after 24 weeks of gestation were enrolled. Influence of maternal age, body-mass-index at the time of the oral glucose tolerance test, parity, smoking, chorionicity, gestational age at delivery and diagnosis of GDM on weight discrepancy of the twins was evaluated. Results: Mean weight discrepancy of all analyzed twin pregnancies was 285 grams (± 231), relative weight discrepancy was 11.3% (± 8.6). Univariate regression analyses showed that GDM, chorionicity and gestational age at delivery were significantly associated with weight discrepancy. In the multivariate model only diagnosis of GDM was significantly associated with weight discrepancy. Conclusion: Twin pregnancies with insulin requiring gestational diabetes seem to have less birth weight discrepancy than twin pregnancies with normal glucose tolerance.