We sought to determine whether Swedish patients with multiple sclerosis (MS) with and without oligoclonal bands (OCBs) in the CSF constitute distinct subpopulations, clinically and immunogenetically. Our findings indicate that OCB-negative MS shares the same clinical features as OCB-positive MS regarding female predominance, age at onset, proportion of primary progressive cases, rate of MRI positivity, and disease severity. Our HLA-DRB1 genotyping results suggest, however, that OCB-positive and OCB-negative MS are immunogenetically distinct.