OBJECTIVES: To evaluate the impact of adherence to inhaled corticosteroids (ICS) on healthcare utilization in patients with asthma. METHODS: IHCIS managed care benchmark database representing over 40 million US commercial lives was analyzed. The first prescription claim for an ICS in 2005 was identified (index date) and patients who were continuously eligible for medical and pharmacy services for 12 month before and after the index date were included. Patients were selected based on the following criteria using the 12 month pre-index date: 1) asthma-related ER use or hospitalization >=1, 2) asthma-related MD visits >= 4, or 3) asthma-related medication fills >=4 and diagnosis of asthma >=1. Adherence was measured using both medication possession ratio - MPR (adherence) and having at least one ICS claim for each of the four post-index quarters (persistence). Healthcare utilization including ER visits and hospitalizations during the post 12 month period was compared between the adherent and non-adherent groups. Poisson regression was utilized to evaluate the impact of adherence with ICS on utilization controlling for potential confounding factors. RESULTS: A total of 18,420 patients 55.8% female with an average age of 31.68 met the criteria for final analyses. Mean MPR was 0.43 and 12.7% of the study population had MPR >= 0.8 (adherent). 44.7 % of patients filled at least one ICS prescription for four consecutive quarters (persistent). Compared to non-adherent patients, adherent patients had significantly less incidence of hospitalization or ER visit (IRR, 0.58; 95% CI, 0.37 - 0.89). Similarly, persistence with ICS prescription filling behavior was associated with a significantly lower incidence of hospitalization or ER visit (IRR, 0.74; 95% CI, 0.62 - 0.87). CONCLUSION: Adherence with ICS was suboptimal in selected patients with asthma. Regardless of metric used, patients identified as adherent were less likely to have an asthma-related hospitalization or ER visit.