A combined retrospective and prospective analysis of 983 hospital patients with Vibrio cholerae infection was carried out in an urban cholera endemic area. The data indicate that despite the complexity of the urban population, certain patterns of infection are discernible. Cholera was seasonal; it had a peak incidence in the dry winter months and almost disappeared during the summer monsoon. The rate of infection was higher in children than adults. The disease did not occur in all parts of the city. Even in the poorer areas, outbreaks tended to localize in small communities which shared facilities for water, food, and sanitation. Multiple members of families were often infected in what appeared to be common-source outbreaks.