BACKGROUND: African Americans (AAs) experience greater disability from multiple sclerosis (MS) compared with Caucasian Americans (CAs). Interethnic immunologic differences in MS and their relationship to disease-related disability have not been described. OBJECTIVE: To compare measures of CSF humoral immunity between AAs and CAs with MS. METHODS: Using a case-control design, all AA MS patients with CSF immune studies at the Washington University MS center were compared with randomly selected CAs with MS. Two CA controls were selected for every AA case. Immunoglobulin G (IgG) index and synthesis rates, oligoclonal band positivity, white blood cell count, and CSF protein were compared between groups. Survival analysis was conducted to compare times to ambulatory assistance. RESULTS: Sixty-six AA cases and 132 CA controls were identified. Measures of CSF humoral activity were all higher in the AA group. The mean IgG index of AAs was 1.35 (SD 0.62), and that of CAs was 1.05 (SD 0.55), for a mean difference of 0.30 (p = 0.001). The median IgG synthesis rate was also higher among AAs (13.55 vs 8.20 mg/day), for a median difference of 5.35 mg/day (p = 0.010). Survival analysis confirmed previous reports of earlier ambulatory assistance requirement among AAs. Despite differences in both humoral immune response and times to ambulatory assistance, Cox proportional hazards modeling did not show IgG index as predictive of earlier ambulatory assistance. CONCLUSIONS: The CSF humoral immune response is more active among African Americans (AAs) than among Caucasian Americans (CAs) with multiple sclerosis. AAs also progress to ambulatory assistance earlier than CAs, but high immunoglobulin G index does not predict earlier progression to the disability endpoint. ©2007AAN Enterprises, Inc.