Although studies have demonstrated relations between obesity and incident asthma, little is known about the association of obesity with acute severity in adults hospitalized for asthma exacerbation. To investigate the association of obesity with acute severity of asthma exacerbation. This is a retrospective cohort study using population-based data of 8 geographically diverse US states from 2010 through 2013. We included adults (age 18-54 years) hospitalized for asthma exacerbation. The outcome measures were markers of acute severity-use of mechanical ventilation (defined by noninvasive positive pressure ventilation and/or invasive mechanical ventilation) and hospital length of stay. To determine the association of obesity with each outcome, we fit multivariable models adjusting for patient-level confounders (eg, age, sex, race/ethnicity, primary insurance, quartiles for household income, residential status, and comorbidities) and potential patient clustering within hospitals. Among the 72,086 patients hospitalized for asthma exacerbation, 24% were obese. Obesity was associated with a significantly higher risk of any mechanical ventilation use (8.3% vs 5.0%; adjusted odds ratio [OR], 1.77; 95% CI, 1.63-1.92; P < .001) driven by the higher risk of noninvasive positive pressure ventilation use (7.2% vs 3.4%; adjusted OR, 2.14; 95% CI, 1.96-2.35; P < .001). Likewise, obese patients were more likely to have a hospital length of stay of 3 or more days compared with nonobese patients (59.4% vs 46.5%; adjusted OR, 1.37; 95% CI, 1.32-1.43; P < .001). These findings were consistent with stratifications by age, sex, and race/ethnicity. In this population-based study of adults hospitalized for asthma exacerbation, obesity was associated with higher acute severity.