OBJECTIVES: Montelukast has been approved for the treatment of seasonal allergic rhinitis. The study's objective was to compare allergic rhinitis (AR) associated medical and pharmacy utilization in asthma patients with comorbid AR initiating inhaled corticosteroids (ICS) or montelukast (MO). METHODS: A retrospective, observational study using healthcare claims from 25 UnitedHealthcare plans was conducted. Subjects less than 65 years old and newly started on either ICS or MO between 01.01.1999 and 12.31.2000 were identified. Subjects with at least one asthma (493.xx) and one AR (477.xx) medical claim, 24 months of continuous enrollment, and either an AR claim or a non-sedating antihistamine (NSA) during the 12-month baseline were included. A logistic propensity score model was constructed utilizing AR, asthma and total health services utilization in the baseline period and matched cohorts selected based on a propensity score difference of £ 0.01. During the 12-month follow-up, the total number of NSA and nasal corticosteroid (NCS) refills, total days supply of NSA received, total AR pharmacy cost (not including asthma medications) and total AR health services cost (pharmacy + medical) were determined. Wilcoxon rank sum was used to test median differences in AR utilization. RESULTS: A total of 1706 subjects were matched, (853 ICS and 853 MO). Compared to ICS subjects, MO subjects received significantly more refills for NSA (median of 2.55 vs. 3.34, p<0.0001), significantly more days of NSA therapy (median days supply of 30 vs. 60, p=0.0001), and fewer NCS refills (median of 0.63 vs. 0.54, p=0.0459). Additionally, MO subjects had significantly higher median AR pharmacy cost ($130 vs. $107, p=0.0028) and total AR cost ($279 vs. $214, p=0.0180). CONCLUSIONS: In this population, compared with ICS, the use of MO in asthma subjects with comorbid AR was associated with greater AR health services cost in the 12-month follow-up period.