The atypical characteristics of primary progressive multiple sclerosis (PPMS) have presented problems in the recruitment to and design of therapeutic trials. The problem areas in the implementation of therapeutic trials are: diagnostic criteria, sample size calculations, and choice of outcome measures. Although there is no definitively proven disease-modifying treatment available for PPMS, several randomized controlled trials have now been specifically designed for this group. The clinical trials in PPMS are based on glatiramer acetate and rituximab. The planned clinical trials in PPMS are based on fingolimod (FTY720) and cladribine. The smaller trials in PPMS are based on Interferon beta-1a, Interferon beta-1b, mitoxantrone and riluzole. A retrospective open-label study of intravenous cyclophosphamide and methylprednisolone in progressive MS included 128 patients with PPMS. PPMS may be the ideal model to investigate disease progression and neuronal protection, and is becoming an important focus for treatment trials in these areas.