Data from routine surveillance during two mass immunisation campaigns (MIC) with Measles-mumps-rubella (MMR)vaccine using Leningrad-Zagreb mumps strain in two states in Brazil were analysed to estimate the risk of vaccine-related meningitis and mumps. Increase in the incidence of the two diseases was observed in both states, 3 weeks after the vaccination campaigns. The estimated number of doses applied per one case of vaccine-related meningitis ranged from 6199 (95% CI: 4854-8058) to 19,247 (95% CI: 12,648-29,513) depending on the diagnostic criteria used and state. It was 300 doses (95% CI: 286-317) for each case of mumps. The implications for vaccination policy are discussed.