BACKGROUND Male sex is a well-known risk factor for unfavorable perinatal outcomes. Fetal sex has been considered only occasionally in diabetic pregnancy. OBJECTIVE Our aim was to evaluate perinatal outcomes in women with gestational diabetes mellitus (GDM) according to fetal sex. METHODS We conducted a retrospective review of all singleton pregnancies of women with GDM progressing to >22 weeks and delivering in our center between 1981 and 2007. Evaluated maternal characteristics included anthropometrics, obstetric history, GDM diagnosis characteristics (ie, gestational age, blood glucose values), HbA(1c) (after diagnosis and in the third trimester). Outcomes variables were cesarean section (CS), gestational hypertension, preterm birth, abnormal Apgar, large and small for gestational age newborns, obstetric trauma, major and minor malformations, neonatal hypoglycemia, jaundice, respiratory distress, polycythemia, hypocalcemia, perinatal mortality, and a composite outcome. We used a descriptive and multiple logistic regression analysis (backwards method). RESULTS A total of 2299 pregnancies were included (1125 female and 1174 male infants). Maternal characteristics were essentially similar in male and female newborns. For outcomes, unadjusted figures were higher in pregnancies of male newborns in 14 of 16 perinatal outcomes, but significance was only reached for CS. The logistic regression analyses revealed male sex as an independent predictor of CS (odds ratio = 1.48; 95% CI, 1.15-1.90) and neonatal hypoglycemia (odds ratio = 2.13; 95% CI, 1.02-4.43). CONCLUSIONS In this group of women with GDM, perinatal outcomes in pregnancies of male newborns differ in only 2 of 16 evaluated variables: an increased frequency of CS and neonatal hypoglycemia. Male newborns of mothers with GDM could benefit from increased awareness of neonatal hypoglycemia.