OBJECTIVE: To evaluate whether maternal obesity is associated with pulmonary and nonpulmonary pregnancy complications in asthmatic women. METHODS: This is a secondary analysis of the prospective cohort Asthma During Pregnancy Study. Asthma patients were classified as having either mild or moderate to severe disease at the beginning of the study. Rates of pulmonary complications of asthma in asthmatic women and rates of nonpulmonary complications of pregnancy among asthma patients and controls, were compared between obese (body mass index ≥ 30 kg/m2) and nonobese women. RESULTS: Maternal body mass index and pregnancy outcome data were available for 1,699 of 1,812 asthmatic women and for 867 of 881 controls. Of the asthma subjects, 30.7% (521) were obese compared with 25.5% of the controls, P = .006. Obese women, regardless of whether they had asthma, were more likely to undergo cesarean delivery (OR 1.6, 95% confidence interval [CI]1.3-2.0) to develop preeclampsia or gestational hypertension (OR 1.7 95% CI 1.3-2.3) and gestational diabetes (OR 4.2, 95% CI 2.8-6.3). There were no differences in the rates of overall asthma improvement (20.6% compared with 23.6%, P = .36) or deterioration (33.3% compared with 28.8%, P = .20) between obese and nonobese asthma patients. After adjustment for confounding variables, obesity, not asthma, was associated with nonpulmonary complications of pregnancy, and obesity was associated with an increase in asthma exacerbations as well (OR 1.3, 95% CI 1.1-1.7). CONCLUSION: Obesity is associated with an increased risk of asthma exacerbations during pregnancy. The increased rate of nonpulmonary complications of pregnancy in asthma patients is associated with obesity in this population and not with asthma status. © 2006 by The American College of Obstetricians and Gynecologists. Published by Lippincott Williams & Wilkins.