Sixty day care centers (DCC) randomly selected from 736 licensed child care facilities in Harris County (Houston), Texas were surveyed for the incidence of diarrhea by periodic visits and weekly telephone calls over two years. A total of 2,708 episodes of diarrhea were reported in 3,800 children under 6 years of age, and 84 cases occurred in center staff. Overall incidence was 0.44 episodes/person/year among children and 0.14 among staff. Attack rates among the 60 DCC ranged from none to 3.64 cases/year in each child. The incidence for children under 36 months of age was 17 times higher than for the older group. Characteristics of DCC associated with higher rates of disease among children were the presence of young, non-bowel trained children, staff who both diapered infants and prepared food on a regular basis, DCC for profit management, and DCC whose only guidelines were provided by the State. The socioeconomic burden associated with DCC disease, its transmission, and control is considerable and needs to be further addressed.