Health care providers need accurate information about all aspects of health care delivery. Clinical trials provide useful information concerning the clinical efficacy of treatment, but they are not representative of the routine conditions with which patients must contend when following treatment regimens. Database studies are being used increasingly to provide information about patient adherence under routine conditions. A retrospective database study was conducted to compare patient adherence and concomitant oral steroid use among patients on oral ?2 agonists or leukotriene antagonist therapy. Consistent with our first hypothesis, patients using antileukotrienes were more adherent than patients on oral ?2 agonists, over a 12-month period. However, contrary to our second hypothesis, patients using antileukotrienes were eight times more likely to be on concomitant oral steroid therapy than patients using oral ?2 agonists. These findings may reflect a “new drug” effect: those patients whose disease is most difficult to control on existing therapies are placed on the newest treatment, drug indications notwithstanding. Finally, we conclude that the results of this study provide further evidence of the utility of retrospective database studies to provide health care providers with cost effective information reflecting real-world patient behaviors. Key Words: Adherence, concomitant therapy, asthma, leukotriene agents.