OBJECTIVE To assess the maternal and fetal complications of pregnancy in mothers with gestational diabetes mellitus (GDM) compared with non-diabetic patients who delivered in the hospital during the study period. METHODS The outcome of pregnancy in 220 Saudi patients with GDM identified from the delivery register/hospital database and matched for age, parity and body mass index with 220 non-diabetic controls were studied retrospectively from their case files. Patients with multiple pregnancies and abnormal presentation of the fetus were excluded from the study. RESULTS The GDM patients were treated with either diet alone or with additional insulin in some patients who required better control of their blood sugar levels. Patients with GDM had a significantly higher incidence of pre-eclampsia (p<0.0001); preterm delivery (p=0.0226); induction of labor (p<0.0001); cesarean section (p=0.0019); higher mean birth weight (p<0.0001) of babies; large for gestational age infants (p=0.0011); macrosomia (p=0.0186); and admission to the neonatal intensive care unit (p=0.0003), compared with the control group. However, the rates of Apgar score <7 at 5 minutes, respiratory distress syndrome, neonatal hypoglycemia, hyperbilirubinemia and the need for phototherapy were similar in both groups of patients. Congenital anomalies and perinatal mortality rates were not significantly different in the two groups. CONCLUSIONS GDM is recognized to be associated with increased rates of adverse maternal and neonatal outcomes, which are supported by the findings of this study. Even the mild form of GDM seems to have significant consequences for women and their offspring and is recommended to be aggressively treated. Evidence suggests that early diagnosis and strict control of blood sugar levels throughout the pregnancy can significantly reduce maternal and fetal complications. A multicenter, randomized controlled trial, based on universally accepted criteria for GDM screening test, standardized diagnostic OGTT and management of all patients with GDM versus the standard obstetric management of the control is warranted.