OBJECTIVE: To assess the effect of a letter-based intervention program, targeted at prescribers and pharmacists, on adherence to national guidelines and healthcare utilization in the Connecticut asthma Medicaid population. METHODS: A retrospective DUR was conducted from April to June 2001. Patients with asthma in the Connecticut Medicaid Program submitting >1 claim per month (over a 6-month period) for short-acting b2-agonists were identified (intervention group; n=135). Patient specific intervention packets explaining the problem, the patient's medication profile, an asthma education leaflet, response form and return envelope were mailed to the patients' prescribers and pharmacists. A control group of asthma patients, who were not HDB users at baseline and drawn from the same Medicaid program, were also identified (n=510). Utilization of long-term asthma control agents and spacers and healthcare utilization were compared between the intervention and control patients 6 months after the mailing. RESULTS: At baseline, the intervention group had lower utilization of long-term control agents compared to the control group (58% vs. 96%, respectively; p <0.001) but there was no difference after the intervention program (65% vs. 71%, p=0.169). A greater number of claims were submitted for spacers in the intervention group compared to control after the mailing (7% vs. 2%, p=0.007). Before the mailing, the intervention group incurred more prescriber office visits than the control group (mean ± SD; 0.46 ± 0.82 vs. 0.25 ± 0.66, p <0.001) but this difference was not evident after the intervention program (0.24 ± 0.63 vs. 0.18 ± 0.60, p=0.283). CONCLUSION: This intervention program had a modest impact on improving the use of long-term control agents and reducing prescriber office visits.