Our objective was to compare adherence to montelukast with adherence to inhaled corticosteroids (ICS) in children with persistent asthma. In this retrospective study, we obtained data from a computerized hospital pharmacy database and medical records on 14l patients, 3-18 years of age, who received care for asthma at a military medical center. For each patient, we collected fill/refill data from a consecutive 6-month period and calculated an adherence rate, i.e., (# doses filled/# doses prescribed) x 100. We then determined whether the patient had "good adherence" (adherence rate, > or =70%) or "very poor adherence" (adherence rate, <50%). Eighty-one children were prescribed montelukast, and 104 took ICS; 44 of these children took both. The majority of patients had mild or moderate persistent asthma. There was no significant difference between mean adherence rates: 71% (95% CI, 65-77%) for montelukast vs. 67% (95% CI, 61-73%) for ICS. Fifty-one percent of patients taking montelukast had good adherence, compared to 41% in the ICS group (P = 0.27). Nineteen percent of the montelukast group and 26% of the ICS group had very poor adherence (P = 0.31). Using pharmacy refill data, we found that children with asthma were no more likely to take montelukast than inhaled corticosteroids. Adherence to both medications was suboptimal, even in a system that provides free and easy access to medications.