The incidence of diarrhea among children in day care centers is highest for those under three years of age. Limited studies indicate that diarrhea occurs more frequently among children enrolled at these centers than among age-matched children cared for at home or in family day care. Most reported outbreaks have been caused by rotavirus, Giardia, Shigella, or combinations of these organisms. Children in day care centers commonly excrete enteropathogens in the absence of symptoms; the significance of this phenomenon in transmission is unknown. An association between higher rates of diarrhea and selected characteristics of centers--the most important of which is the presence of non-toilet-trained children--has been shown. The contamination of hands, communal toys, and other classroom objects as well as a lack of infection control measures play a role in the transmission of enteropathogens in outbreaks of diarrhea in day care centers. Spread of infection from non-toilet-trained children in centers to their families is common. Potential ways of dealing with this situation include education; development, implementation, and enforcement of regulations; and use of infection control measures. However, the effectiveness of specific control measures has not been systematically evaluated.