An outbreak of gastroenteritis due to a small round structured virus (SRSV) (Norwalk-like virus) occurred in an elderly care unit, affecting a total of 126 patients and staff. The outbreak caused major disruption to the provision of health care services by the unit over a 3-week period. Following the outbreak a study was undertaken to explore risk factors for acquisition of SRSV infection by health care workers on the unit. Exposure to patients nearby who were vomiting and the number of close contacts with ill patients were significantly related to the risk of developing gastroenteritis (P < 0.05). No significant increase in risk of developing gastroenteritis was found in nurses who cleaned vomit or faeces from affected patients. The findings suggest that aerosolization of vomit was of major importance in transmission of infection during the outbreak; the implications for infection control are discussed.