Risk factors for proliferative enteropathy were investigated by means of a postal questionnaire survey of randomly selected British pig farms. Replies were received from 319 (56 per cent) of the 569 questionnaires posted, representing 1.5 per cent of the total number of pig farms in Britain. Thirty-one per cent of the farms had experienced at least one episode of proliferative enteropathy within the previous three years, usually confirmed by their veterinary surgeon. There was a strong association for the occurrence of proliferative enteropathy in herds of over 500 sows (P<0.005) and in herds with enzootic pneumonia (P<0.01). Outbreaks had occurred in five of the six nucleus herds surveyed, the other had only 80 sows. Outbreaks occurred in 32 of 69 herds that had obtained their replacement boars from nucleus herds (P<0.05), suggesting that infected boars may carry the disease into distant herds. The use of either fully slatted (P<0.05) or fully meshed floors (P<0.01) above sunken pits in buildings used to house pigs immediately after weaning, and the use of partially (P<0.05) or fully slatted floors (P<0.05) in buildings used to house pigs two to six months old, were risk factors for outbreaks of proliferative enteropathy, compared with the use of straw bedding or solid floors. The destocking of entire buildings containing pigs two to four months old before the introduction of fresh pigs, was associated with a reduced risk (P<0.05), but the destocking of selected pens rather than the whole building had no such association. The type of diet, or feeding or watering system and the types of buildings used were not identified as risk factors.