Asthma complicates up to 4% of pregnancies. Our objective was to compare emergency department (ED) visits for acute asthma among pregnant versus nonpregnant women. We performed a prospective cohort study, as part of the Multicenter Asthma Research Collaboration. ED patients who presented with acute asthma underwent a structured interview in the ED, and another by telephone 2 wk later. The study was performed at 36 EDs in 18 states. A total of 51 pregnant women and 500 nonpregnant women, age 18 to 39, were available for analysis. Pregnant women did not differ from nonpregnant women by duration of asthma symptoms (median: 0.75 versus 0.75 d, p = 0.57) or initial peak expiratory flow rate (PEFR) (51% versus 53% of predicted, p = 0.52). Despite this similarity, only 44% of pregnant women were treated with corticosteroids in the ED compared with 66% of nonpregnant women (p = 0.002). Pregnant women were equally likely to be admitted (24% versus 21%, p = 0.61) but less likely to be prescribed corticosteroids if sent home (38% versus 64%, p = 0.002). At 2-wk follow-up, pregnant women were 2.9 times more likely to report an ongoing exacerbation (95% CI, 1.2 to 6.8). Among women presenting to the ED with acute asthma, pregnant asthmatics are less likely to receive appropriate treatment with corticosteroids.