We investigated the impact of maternal obesity on pregnancy outcomes. Women with normal or obese body mass index (BMI) who delivered singleton infants at term were identified from a perinatal database. Rates of pregnancy complications and neonatal outcomes were compared between women with normal prepregnancy BMI (20 to 24.9 kg/m (2), N = 9171) and those with an obese prepregnancy BMI (> or = 30, N = 3744). Rates of pregnancy complications and neonatal outcomes were also evaluated by the level of obesity (obese [30 to 34.9 kg/m (2), N = 2106], severe obesity [35 to 39.9 kg/m (2), N = 953], and morbid obesity [> or = 40 kg/m (2), N = 685]). Rates of gestational diabetes (12.0% versus 3.7%, P < 0.001, odds ratio [95% confidence interval] = 3.5 [3.0, 4.1]) and gestational hypertension (30.9% versus 9.0%, P < 0.001, odds ratio [95% confidence interval] = 4.5 [4.1, 5.0]) were higher for obese versus normal BMI gravidas, respectively. Women with morbid or severe obesity had a greater incidence of gestational diabetes than women with an obese (30 to 34.9 kg/m (2)) or normal BMI (14.1%, 16.4%, 9.6%, and 3.7%, respectively; P < 0.05). The incidence of gestational hypertension increased with maternal BMI (9.0% normal, 25.5% obese, 33.7% severe, 43.4% morbid; all pairwise comparisons P < 0.05). Obese versus normal BMI was associated with more higher-level nursery admissions (8.2% versus 5.8%) and large-for-gestational age infants (12.3% versus 6.5%; P < 0.001). Obesity places a term pregnancy at risk for adverse maternal and neonatal outcomes.