Asthma-related hospitalization rates were compared over a 2-year period between a cohort of patients with asthma who switched from an inhaled corticosteroid in year 1 to a leukotriene modifier in year 2 (n = 285) and a matched cohort continuously treated with an inhaled corticosteroid (n = 570). During year 1, patients were well maintained, with a hospitalization rate of 1.1% to 1.4%. During year 2, 2.5% of the patients switched to a leukotriene modifier had one or more asthma-related hospitalizations compared with 0.6% of the patients continuously receiving an inhaled corticosteroid. Patients treated with a leukotriene modifier were at 7 times greater risk for an asthma-related hospitalization compared with patients who continued to receive an inhaled corticosteroid (risk-adjusted odds ratio, 7.1; 95% CI, 2.79-17.95). These data are consistent with the results of well-controlled clinical trials showing that leukotriene modifiers may be associated with deterioration of asthma control relative to inhaled corticosteroids. Considered in aggregate, the data support the conclusion that leukotriene modifiers should not be substituted for inhaled corticosteroids as a single-controller therapy for asthma. (J Allergy Clin Immunol 2002;110:39-41.)