Purpose: To examine the impact of gestational diabetes mellitus (GDM) on maternal-fetal outcomes in Manitoba. Methods: The rates of macrosomia, stillbirth, cesarean section (C/S) and shoulder dystocia (S/D) in 324,605 births in Manitoba during 1985-2004, and their relationships with diabetes and demographical factors were analyzed. Results: The incidence of macrosomia, stillbirth, C/S and S/D were 15.3%, 0.57%, 16.0%, and 1.2%, respectively. The rates of macrosomia were elevated in mothers with GDM, type 2 DM (T2DM), rural living, First Nations (FN) status, or ?35 years of age. Increased rates of stillbirth were associated with women with T2DM, FN status or ?35 years, but not those with GDM. C/S and S/D were increased in women with GDM or T2DM. FN status in combination with GDM increased the risk of S/D. Conclusions: GDM, T2DM, advanced maternal age, FN status or rural living affected pregnancy outcomes in Manitoba.