The pattern of cholera in an endemic area of rural East Pakistan is described. Cholera has a definite season, with most cases occurring during December and January. There is sometimes a second epidemic in May, June, and July. Although the area is considered to be endemic for cholera, the infection was not detected for periods varying from 2 to 5 months. The disease is widely disseminated. The entire area appears to become involved at once with little evidence of village-to-village spread suggesting multiple simultaneous introductions of the disease. The age specific attack rate is highest in the under 5-year age group and declines with age. The attack rate is higher among Hindus than among Muslims. Mild cases of cholera which do not require hospitalization are most likely to occur in children under the age of 5. Within the families of cholera patients, the secondary infection rate is highest in young children.