From October 1, 1990, until April 28, 1991, 13 578 cases of measles were reported in the urban community of Niamey, Niger. Vaccine coverages (one dose of Schwarz vaccine given after 9 months) in urban community of Niamey were, respectively, 63% at the age of 12 months and 73% at 24 months before the epidemic. Incidence rates were the highest among children ages 6 to 8 months and 9 to 11 months and 22% of the cases were less than 1 year old. Vaccine efficacy estimates ranged from 86 to 94% according to age groups and the method used (screening method, case control study, retrospective cohort study). The risk of transmission of illness increased with the intensity of contact with a case. Contact with a health facility 7 to 22 days before onset of rash was not a risk factor. Seasonal migrants in Niamey were more likely to develop measles. Recommendations included implementation of an early two dose schedule of measles immunization during the outbreak, vaccination offered at each contact with a health facility, radio and television advertising for measles immunization and distribution of vitamin A to all measles cases.