This retrospective study was conducted in the UK and identifies the most frequent causes, diagnoses, treatment and prognoses for short- and long-term survival in 54 cases of horses with haemoperitoneum. Clinical signs of haemorrhagic shock and colic were common, and abdominal ultrasound was very useful for the identification of haemoperitoneum. Causes of haemoperitoneum included uterine injury (22 per cent), involvement of specific blood vessels (20 per cent), splenic injury (19 per cent), neoplasia (13 per cent) and other (4 per cent). No source was identified in 22 per cent of cases. Fifty-seven per cent of cases underwent exploratory laparotomy. Of the surgical cases, a diagnosis was made in 65 per cent, with 42 per cent surviving to discharge. It was felt that exploratory laparotomy had both diagnostic and therapeutic implications. Twenty-eight per cent of cases died, and 33 per cent were euthanased, whereas 39 per cent survived to be discharged from the hospital, with 35 per cent of these surviving in the long term. Idiopathic haennoperitoneum was associated with the best outcome for long-term survival.