Recombinant interferons have been shown to suppress both the clinical and magnetic resonance imaging (MRI) measures of disease activity in patients with relapsing remitting multiple sclerosis (RRMS).We performed a Cochrane review of all randomised, placebo-controlled trials of recombinant interferons in RRMS.Of 208 articles identified by a predefined search strategy, seven of these, reporting randomised trials, met all the selection criteria and form the subject of this review.The trials selected were double-blind, placebo-controlled, randomised trials of RRMS patients who were treated with recombinant interferon, given by the subcutaneous or the intramuscular route.The quality of the trials was variable, with substantial methodological inadequacies in allocation concealment, high proportion and incomplete description of dropouts and failure to adhere to the principles of intention to treat analysis. The baseline characteristics were largely comparable between treatment and placebo groups. Because of prominent treatment-associated side effects, which could be easily identified by patients, these trials could be considered as single blind rather than double-blind.Although 1215 patients were included in this review, only 919 (76%) contributed to the results concerning exacerbations and progression of the disease at two years. Specifically interferon significantly reduced the occurrence of exacerbations (RR =0.80, 95% CI [0.73,0.88], p<0.001) and progression of the disease (RR =0.69, 95% CI [0.55,0.87], p= 0.002) two years after randomisation. However, the correct assignment of dropouts was essential to the demonstration of efficacy, most conspicuously concerning the effect of the drug on disease progression. If interferon-treated patients who dropped out were deemed to have progressed (worst case scenario) the significance of these effects was lost (RR = 1.31, CI [0.60,2.89], p = 0.5). The evolution in magnetic resonance imaging (MRI) technology in the decade in which these trials were performed and different reporting of data among trials made it impossible to perform a quantitative analysis of the MRI results. Both clinical and laboratory side effects reported in the trials were more frequent in treated patients than in controls. No information was available regarding side effects and adverse events after two years of follow-up. The impact of interferon treatment (and its side effects) on the quality of life of patients was not reported in any trial included in this review.The efficacy of interferon on exacerbations and disease progression in patients with relapsing remitting MS was modest after one and two years of treatment. It was not possible to conduct a quantitative analysis beyond two years. Longer follow-up and more uniform reporting of clinical and MRI outcomes among these trials might have allowed for a more convincing conclusion.