OBJECTIVES: This study analyzed managed care claims to find out how zafirlukast, a recently established oral asthma therapy, is being prescribed in clinical practice and to evaluate the effects of zafirlukast therapy on healthcare resource utilisation. METHODS: We examined the claims of 780 patients (>12 years) who participated in a Northeastern US managed care plan and had received at least 3 months’ therapy with zafirlukast, including at least one repeat prescription. Baseline medications were determined 3 months before the start of zafirlukast. Use of healthcare services, including number of outpatient visits, inpatient stays, emergency department visits, and asthma-related drug prescriptions, were compared between 3 months before and 3 months after commencing zafirlukast. RESULTS: Zafirlukast was prescribed to patients on a variety of baseline medications, with 72% already receiving inhaled corticosteroids. Within 3 months of starting zafirlukast, outpatient visits, inpatient stays, emergency department visits, and albuterol prescriptions were all significantly reduced compared with the previous 3 months (p<0.002). In the 3 months before starting zafirlukast, 55% of patients received oral corticosteroids, compared with <15% in the 3 months after commencing zafirlukast. CONCLUSIONS: Retrospective data analysis may be valuable in determining how therapies are used in clinical practice and in measuring the effectiveness of asthma therapies outside of controlled clinical trials. This study shows that the addition of zafirlukast to existing asthma regimens was associated with reduced healthcare utilisation and reduced need for oral corticosteroids and albuterol, which may translate into reduced direct healthcare costs.