BACKGROUND: Two doses of measles vaccine (MV) might reduce the nonmeasles mortality rate more than 1 dose of MV does. The effect of 2 versus 1 dose on morbidity has not been examined. Within a randomized trial of the effect of 2 doses versus 1 dose of MV on mortality in Guinea-Bissau, we investigated the effect on hospital admissions. METHODS: Children were randomly assigned 1:2 to receive MV at 4.5 and 9 months of age or the currently recommended dose at 9 months. We compared hospital admission rates among children between 9 and 18 months of age in a Cox regression model with age as the underlying time scale. Half of the children had received neonatal vitamin A supplementation (NVAS) in another trial. The beneficial effect of MV at 4.5 and 9 months on mortality was limited to children who had not received NVAS; therefore, we investigated the interaction of MV with NVAS on admission rates. RESULTS: Among 5626 children (2 doses of MV, 1960 children; 1 dose of MV, 3666), we identified 311 hospital admissions of children between 9 and 18 months of age. Overall, compared to 1 dose of MV, 2 doses reduced the risk of hospital admission for children who had not received NVAS (hazard ratio [HR], 0.66 [95% confidence interval (CI), 0.47-0.93]), but we found no effect among NVAS recipients (HR, 1.16 [95% CI, 0.82-1.63]) (P = .02 for interaction). CONCLUSIONS: The benefit of 2 doses of MV was limited to children who had not received NVAS. NVAS is not generally recommended; hence, an early 2-dose measles vaccination policy might reduce hospital admissions more than the current policy of providing the first MV at 9 months of age. TRIAL REGISTRATION: ClinicalTrials.gov identifier NCT00168558.