Estimates of the beta-interferon (IFNB) stopping rate in relapsing-remitting multiple sclerosis (RRMS) and secondary progressive MS (SPMS) vary and have been mainly derived from multicentre studies. This is a retrospective, hospital chart-based study of 394 patients treated by a single neurologist for up to eight years. The aims of the study were to ascertain the frequency and timing of IFNB discontinuation in a well supported cohort, and to investigate whether the clinical disease type at the initiation of IFNB or the reason for discontinuation influenced stopping rates. The median follow-up was 49 months. The overall IFNB stopping rate was 28% over five years; there was a significant difference between the IFNB stopping rates for RRMS (14%) and SPMS (23%) after three years of follow-up (P =0.0003). Patients stopped IFNB due to side effects after a median of 13 months, and due to failure of therapy after a median of 35 months (P =0.0004). Significantly more patients with SPMS than with RRMS stopped IFNB due to treatment failure (P =0.037). IFNB discontinuation occurred earlier in the treatment course when due to side effects. Stopping IFNB therapy was more common in SPMS and was more often due to treatment failure than side effects.