OBJECTIVE: To examine the impact of glatiramer acetate (GA) versus beta interferons 1a (1A) and 1b (1B) on relapse rates as well as utilization and costs among patients with multiple sclerosis (MS) in a managed care setting. METHODS: Data were obtained from a national retrospective database of patient-linked medical and pharmacy claims from January 1996 to June 2001. Patients were followed from the first prescription for immunomodulatory therapy until plan disenrollment or end of study timeframe. The incidence of all relapses (defined as hospitalization for MS or ambulatory visit followed by use of systemic corticosteroids) as well as utilization and costs of MS-related care were examined for each group. Data were adjusted for variable follow-up using survival techniques; the risk of relapse was evaluated using a Cox proportional hazards model. RESULTS: A total of 8,457 patients receiving immunomodulatory therapy were included in the study cohort (1,674, 5,031, and 1,752 for GA, 1A, and 1B respectively); follow-up averaged 17.3 months. Three-quarters of patients were female; the mean age was 42.2 years. The risk of relapse at one year post-therapy initiation was significantly increased for the beta interferons relative to GA (hazard rates: 1.15 and 1.51 for 1A and 1B respectively, p<0.01). Mean (SD) costs of care at one year of follow-up also were reduced among GA patients ($9,522 [$9,706] vs. $9,957 [$9,083] and $10,185 [$9,526] for 1A and 1B respectively). Findings persisted in multivariate analyses controlling for differences in demographic characteristics and propensity scores for immunomodulatory therapy. CONCLUSIONS: Glatiramer acetate is associated with reductions in the incidence of relapse and costs of care relative to the beta interferons among this large group of managed-care patients with MS.