Studies of measles mortality have continued for several years in an urban area of Guinea-Bissau. The case-fatality ratio has been as high as 15% despite a relatively good state of nutrition in the community. Mortality has been significantly higher for secondary cases in houses with several cases than for index cases. Of the deaths from measles, 85% have been the result of secondary cases. Sociocultural institutions such as multifamily dwellings, which foster close contact of many susceptible children, increase the risk of measles mortality.