Forty seven cases of poliomyelitis and 94 controls were studied for immunization status. Unmatched analysis with one control per case and two controls per case was done to find out the ratio of the odds of immunization in diseased individuals as compared with the nondiseased (odds ratio). This ratio (OR) was used further to calculate oral polio vaccine efficacy. OPV efficacy was found to be 93% with 95% confidence limits of 75-98%.