Background Obesity in pregnancy is increasing worldwide, reaching epidemic proportions in many countries and frequently creating challenges for obstetricians. We conducted this study to assess the effects of maternal obesity on maternal and perinatal outcomes. Methods A historical cohort study was performed on 16,609 women who delivered singleton babies in a 5-year period (2013–2017). Data were retrieved from the Cruces Perinatal Database (CPD) and only women whose prepregnancy body mass index (BMI) was known were included. Women were categorized according to the World Health Organization (WHO) classification: normal weight (BMI 20–24.9 kg/m 2 ) and obesity (BMI ≥ 30 kg/m 2 ). Obstetric, perinatal and neonatal outcomes were compared, and adjusted odds ratios (aORs) and 95% confidence intervals (95% CIs) were calculated using the normal-weight group as the reference. Results Compared to women of normal weight (n = 9778), obese women (n = 2207) had a higher risk of preeclampsia (aOR 2.199, 95% CI: 1.46–3.29), rectovaginal group B streptococcus colonization (aOR 1.299, 95% CI: 1.14–1.47), induction of labor (aOR 1.593, 95% CI: 1.44–1.75), cesarean section (aOR 2.755, 95% CI: 2.46–3.08), cesarean section in women with a history of cesarean delivery (aOR 1.409, 95% CI: 1.03–1.92), fetal weight ≥4000 g (aOR 2.090, 95% CI: 1.803–2.422) and admission to the neonatal intensive care unit (NICU) (aOR 1.341, 95% CI: 1.12–1.59). No association was found with preterm birth (aOR 0.936, 95% CI: 0.77–1.13), stillbirth (aOR 0.921, 95% CI: 0.41–2.02) or neonatal mortality (aOR 2.205, 95% CI: 0.86–5.62). Conclusion Maternal obesity is associated with a higher risk of adverse pregnancy and perinatal outcomes. Pregnancy in this population of women should be considered and managed as high risk.