In an urban area of Guinea-Bissau, 384 children were enrolled in a randomized trial comparing morbidity and mortality rates after receiving high-titer Edmonston-Zagreb (EZ) measles vaccine administered from 4 months of age, with a control group receiving inactivated poliomyelitis vaccine at 4 months of age and the standard Schwarz vaccine from 9 months of age. Children were followed to the age of at least 3 years. The mortality ratio of the EZ vaccinees compared with control subjects was 1.79 (range, 1.06 to 3.02; p = 0.027) if children were excluded at the time of migration; if deaths after migration were included, the mortality ratio was 1.53 (range, 0.94 to 2.49; p = 0.087). Girls in the EZ group had significantly higher mortality rates than girls in the control group (mortality ratio = 1.95; range, 1.07 to 3.56; p = 0.027); there was no difference for the boys (mortality ratio = 0.98; range, 0.41 to 2.30). Adjustment for background factors in a Cox regression model did not modify these estimates. Furthermore, female recipients of EZ vaccine had more days with diarrhea (relative risk = 1.35; range, 1.17 to 1.56; p = 0.00003) and were more likely than control subjects to visit a health center in the month after vaccination (relative risk = 1.86; range, 1.05 to 3.31; p = 0.027); those who consulted were more likely to die subsequently (mortality ratio = 2.31; range, 0.99 to 5.41; p = 0.054). These observations were unplanned and require confirmation in larger studies.