Background: In the United States, the prevalence of asthma is not only higher than in most other countries, it also varies greatly between diverse populations. Only limited data exist that examine the variation of outcomes by gender in patients admitted to a hospital for asthma.Objective: This study assessed outcome differences based on gender in adults who were admitted nationally with the primary diagnosis of asthma.Methods: A retrospective cohort study was conducted of all patients who were admitted to a hospital with the primary diagnosis of asthma in 2002-2005 and were reported in the Nationwide Inpatient Sample of the Healthcare Cost and Utilization Project. Patients were excluded if they were aged <18 years or had an additional diagnosis of chronic obstructive pulmonary disease.Results: A total of 590,410 patients (439,991 women, 150,419 men) were included in the study. Patients admitted for asthma were significantly more likely to be female (P < 0.05). Women were significantly older compared with men (mean [SD], 48.5 [17.4] vs 44.6 [17.0] years, respectively), had a longer length of stay (3.44 vs 2.84 days), were more likely to be white (37.9% vs 34.2%), and had a higher total cost of admission ($10,575 vs $9390) (all, P < 0.05). Women were more likely than men to need a tracheostomy (adjusted odds ratio [AOR] = 2.04; 95% CI, 1.77-2.35) and to have a bronchoscopy (AOR =1.12; 95% CI, 1.05-1.21). Men were significantly more likely than women to have arterial blood gases performed (AOR = 1.15; 95% Cl, 1.05-1.27) and to be intubated (AOR = 1.18; 95% Cl, 1.10-1.26) (both, P < 0.05). Men were significantly more likely to be admitted as an emergency admission (AOR = 1.10; 95% Cl, 1.04-1.18) and to die during hospitalization (AOR =1.69; 95% CI, 1.41-2.03).Conclusion: Although they were less likely to be admitted to a hospital, men were more likely to be admitted as an emergency and to experience worse outcomes compared with women, in this study of adults with asthma in the United States.