Recently, a placebo-controlled multicentre randomised clinical trial was published on the efficacy of interferon beta-Ib in the treatment of secondary progressive multiple sclerosis. The study was stopped after the interim analysis because evidence of efficacy was already clear. However, the results appear to be considerably less convincing. The decision to prematurely stop the clinical trial was based more on an overestimate of the p-values than on the clinical relevance of the treatment effects. The efficacy of interferon should be investigated in relation to other treatment options, such as immunoglobulin, copolymer I, azathioprine and methotrexate.