Recent studies have suggested faster clinical progression and greater disability in multiple sclerosis patients of African descent. This study analysed the effect of ethnicity on progression and disability. Sixty-five patients with primary progressive multiple sclerosis were selected and classified as being of African descent or white. Time from onset of the disease until reaching Expanded Disability Status Scale grades 3, 6, and 8 was assessed, as well as irreversible disability (Expanded Disability Status Scale grade maintained for >or=6 months). In the African descent group, the median time to reach Expanded Disability Status Scale 3 was 1 year shorter (1 year vs 2 years, p= 0.02), and to reach Expanded Disability Status Scale 6 was 2 years shorter (3 years vs 5 years, p= 0.01) than in the group of white patients. According to the Kaplan-Meier survival curves, patients of African descent reached every disability stage faster than white patients (p= 0.03, p = 0.04, and p = 0.03, respectively, for Expanded Disability Status Scale grades 3, 6, and 8). As in United States and European patients of African descent, the more severe and faster progression of multiple sclerosis seen in Brazilian primary progressive multiple sclerosis patients of African descent suggests a possibly greater effect of ethnicity rather than environment on the progression of multiple sclerosis.