This independent, population-based surveillance study monitored, in clinical practice, the efficacy of interferon beta (IFNbeta) products in 1173 patients with multiple sclerosis (MS) from the Department of Neurological and Psychiatric Sciences, University of Bari, Italy. Relapses and Expanded Disability Status Scale (EDSS) scores were evaluated for up to 6 years for Avonex, Betaferon and Rebif 22 groups, and for up to 3 years for the Rebif 44 group. IFNbeta products produced significant reductions from baseline in relapse rates at 2, 4 and >4 years (p<0.0001), with no differences among treatments (p=0.2). A modest significant (p<0.05) increase of EDSS was observed in all treatment groups from baseline to 48 months, followed thereafter by a plateau. The IFNbeta-1b group showed more withdrawals (19%) compared with Avonex (6%) and Rebif (7%) at 6 years.