OBJECTIVE To determine the magnitude of relapses in multibacillary leprosy patients after multi-drug therapy and to determine the factors influencing the relapse. METHODS A retrospective study pertaining to multibacillary leprosy patients treated with MBMDT as per WHO guidelines was carried out. The study included 300 MB patients who had successfully completed treatment during 1986-2002, of whom 163 patients were available for follow-up. Patients were examined clinically and bacteriologically to asses the present status of disease. RESULTS A total of three cases relapsed at 2, 4 and 11 years after being released from treatment which gives a crude cumulative relapse rate of 1.84% for the 18 year period of follow-up with mean duration of follow-up 7.13 +/- 1.25 years. It also gives the total follow-up period of 1163 person-years with the relapse rate of 0.26/100 person-years of follow-up (95% confidence interval is 0.235-0.285). CONCLUSIONS Relapse rate after WHO recommended MDT leprosy is low. High bacterial load before initiation of therapy is an important factor which determines the relapse.