Despite having a chronic respiratory disease, adults with asthma do not appear to selectively avoid smoking. We used data from a prospective cohort study of 865 adults, with asthma recruited from a large managed care organization after hospitalization for asthma. In this study, we analysed the association between cigarette smoking and asthma health outcomes, controlling for age, sex, race, educational attainment, household income, atopic history, and history of childhood asthma onset. Current smoking was associated with increased severity of asthma (mean increment, 1.36 points; 95% CI=0.36, 2.36), worse asthma-specific quality of life (mean score increment, 5.49 points; 95% CI=0;2.19, 8.78), and worse generic mental health status (mean score decrement, –4.57 points; 95% CI=–7.01, −2.12); p<.05 in all cases. Current smoking also was associated with a greater longitudinal risk of hospitalization for asthma (OR=1.86, 95% CI=1.03, 3.36). Our results suggest that the pubic health consequences of smoking, in terms of additional asthma morbidity, are considerable. Smoking is a modifiable risk factor for adverse asthma health outcomes. Public health interventions should focus on smoking reduction among adults with asthma.