An increase in the number of preschool children cared for within groups in child care centres has been associated with increasing numbers of women in the workforce. Children at this age are at high risk for gastrointestinal diseases caused by a large number of enteric pathogens, and the risk is increased by the greater potential for person-to-person transmission within group care. This report considers the pathogens that may cause diarrhoeal illness in children, with particular reference to those that have been reported in formal day care settings. The major risk factors for transmission of these agents and a high rate of diarrhoeal illness in the child care setting include attendance of non-toilet-trained children, staff combining nappy changing and food preparation duties, large enrollment, low staff-to-child ratio, and poor hygiene and child handling practices. Investigations undertaken during an outbreak of diarrhoea have frequently used limited diagnostic testing, often suitable for identifying only bacterial and protozoal agents. Such limited investigations have tended to incriminate agents that have prolonged carriage and are easily identifiable in standard microbiology laboratories. Finding a pathogen in these circumstances needs to be interpreted with caution. Prevention and control measures include training and education in good personal hygiene, emphasis on the need for frequent handwashing, separation of change areas from food handling and eating areas, routine cleaning and disinfection of environmental surfaces and personal items, and exclusion of any child or child care worker with diarrhoea.