A prospective survey of the use of high and medium-titre measles vaccine in Guinea-Bissau, the Gambia, and Senegal indicated that this regimen is associated with higher long-term child mortality than the standard titre vaccine. Children enrolled in trials in these three countries received medium or high-titre vaccines at three months of age and survival data were compared to findings from controls who received the standard titre at nine months of age. There were 339 deaths among the 3073 children (11,129 child-years) followed for up to three years of age. Combination of all West African data for medium and high-titre vaccines yielded a mortality rate of 1.21 (95% confidence interval, 0.89-1.63). The excess mortality was statistically significant at the p 0.05 level only when high-titre vaccine was compared to the standard regimen (1.33; 95% confidence interval, 1.02-1.73). No difference in mortality was found between medium or high-titre recipients and control children who had not yet received any vaccine. The excess mortality in the high-titre groups was restricted to females. There was no interaction between age and vaccine type. As a result of these findings, the World Health Organization reversed its 1989 recommendation for use of high-titre measles vaccine. Urged are community studies of measles-related morbidity and mortality that investigate the gender differential identified in this survey.