To assess maternal and perinatal complications associated with mild gestational hyperglycemia (MGH). This retrospective study was conducted in the perinatology division of Zekai Tahir Burak Women's Hospital between January and June 2009. Four hundred and eighty one patients with MGH and 212 patients with pre-gestational diabetes or gestational diabetes mellitus (GDM) were recruited in the study. The control group consisted of 479 patients with normal glucose challenge test. Patients with MGH and the control group were compared in terms of maternal and neonatal complications. The rates of large-for-gestational-age (LGA) or macrosomic infants, pregnancy induced hypertension, primary cesarean delivery, preterm delivery and neonatal hypoglycemia were significantly higher in patients with MGH, GDM or preexisting diabetes. The rates of spontaneous preterm labor, shoulder dystocia, hyperbilirubinemia, low 1-min Apgar score, fetal malformations and neonatal morbidity did not differ between the groups. MGH is associated with an increased risk of primary cesarean delivery, preterm delivery, pregnancy induced hypertension, and macrosomic and LGA infants.