We have studied the clinical, radiological and pathological features of three patients with recurrent massive lower gastrointestinal arterial haemorrhage. Case 1 was an example of Dieulafoy's vascular malformation within the proximal ascending colon in a 46-year-old woman. Cases 2 and 3 were men aged 81 and 83 years with arterial erosions contained within small mucosal diverticula in the hepatic flexure and descending colon, respectively. All three patients presented with recurrent acute episodes of massive lower gastrointestinal haemorrhage. Selective mesenteric angiography was performed in cases 1 and 3 to localize the bleeding point in both patients. The features were very different to those of angiodysplasia, lacking the tuft of abnormal vessels and the early venous filling phase commonly seen in the latter condition. The patients were all successfully treated by partial colectomy. The aetiology of Dieulafoy's vascular malformation remains unclear. The ruptured arteries in cases 2 and 3 shared many histological features with the Dieulafoy lesion in case 1. The lesions in cases 1 and 2 were associated with recent oral non-steroidal anti-inflammatory therapy, suggesting coincidental mucosal ulceration as a contributory factor.