Adherence to long-term therapy has always been a problem in all fields of medicine. In multiple sclerosis (MS), treatment consists of parenteral administration of immune-modulating drugs once or several times weekly for an as yet undetermined length of time. Different studies on the MS patients' compliance showed that the most frequent cause of stopping treatment is the perceived lack of efficacy and that most treatment withdrawals occur during the first year of treatment. A trial aimed to identify the minimum effective IFNbeta dose showed that some patients had disease activity after switching to a lower IFNbeta dose. OPTIMS (OPTimization of Interferon dose for MS study) was a multicenter study, involving 24 Italian MS centers, 216 patients, aimed to identify a treatment response indicator allowing the early identification of poorly responding patients. A single active scan during the first 6 months of IFN treatment had a significant positive predictability of 59% (95% confidence interval, 41-76; p=0.05) on the presence of clinical signs of disease activity during the further 2-year follow-up.