Eighty of the 460 patients and staff (attack rate 22%) in a long-stay hospital for patients with learning difficulties became ill in a general outbreak of gastrointestinal infection that followed a buffet style party on one ward. Illness in the cohort of 47 resident patients, relations, and staff who attended that party was associated with having eaten ham, coleslaw, bread rolls, and cheese and pineapple on sticks. Food from the hospital kitchen was supplemented by food brought in and prepared on the ward by staff and patients. The investigation suggested that food items were contaminated either during preparation by staff and patients or during the party when people served themselves. Microbiological and virological investigations were negative, but small round structured virus was thought to be responsible. Hospitals could do more to prevent outbreaks of foodborne infection by undertaking risk assessment as required by the Food Safety Act (General Food Hygiene) Regulations 1995. Purchasers of hospital infection control should ensure compliance with this legislation.