Measles control remains a great challenge in Uganda. We conducted a prospective study among household contacts aged 9-59 months to assess measles vaccination effectiveness. Index cases were measles patients seen in Kampala hospitals in 1999. Measles was diagnosed in 37/43 (86%) of unvaccinated and in 33/145 (23%) of vaccinated exposed contacts, respectively. Vaccination effectiveness was 74% (95% CI; 64-81), which was lower than expected. This may indicate the need for strengthening of the cold chain and/or introduction of a second opportunity for measles vaccination, either as part of the routine immunization program or in the form of supplementary immunization activities.