SUMMARY Hepatic artery aneurysms occur infrequently and are often difficult to diagnose. Non-invasive procedures such as ultrasound or computer assisted tomography have not been considered suitable for definitive diagnosis and angiography is usually required. A patient is described in whom a mycotic hepatic artery aneurysm developed during the course of subacute bacterial endocarditis. The definitive diagnosis was made using computer assisted tomography with intravenous contrast enhancement and angiography was undertaken only as a prelude to transcatheter embolisation. The same technique was used to monitor progress after embolisation precluding the need for follow up angiography. As 80% of patients with hepatic artery aneurysm present for the first time after aneurysm rupture, the mortality associated with this condition is high. More widespread use of intravenous contrast enhanced tomography for abdominal examination in patients with unexplained abdominal pain might result in earlier diagnosis of this condition.Hepatic artery aneurysms occur infrequently and are often difficult to diagnose. In many patients the diagnosis is only made after aneurysm rupture so that only one patient in five with this condition survives even today. Until now angiography has been considered essential for the diagnosis; accurate, non-invasive methods of investigation might allow for earlier diagnosis and intervention. We describe a patient in whom the diagnosis of mycotic aneurysm of the the hepatic artery was made using computer assisted tomography (CAT) with intravenous contrast enhancement obviating the need for diagnostic angiography. The same procedure was used for monitoring the lesion after transcatheter embolisation. was treated with a variety of non-steroidal antiinflammatory agents but with little effect. During this time his general condition deteriorated, he lost 12.7 kg in weight and developed right upper quadrant pain. In May 1983 he was admitted to hospital for further investigation.On examination he was cachectic, his temperature was 38°C and several joints were painful and swollen. He had a collapsing pulse and an early diastolic decrescendo murmur at the left sternal edge together with a diastolic murmur in the mitral area: there were no signs of cardiac failure and the rest of the examination was unremarkable.Initial investigations showed the following: haemoglobin 8-3 g/dl (reference range 13-0-17-5 g/dl), white cell count 10 400x109/l (4-11,OOOx 109/l), ESR 125 mm/h (<17 mm/h), serum bilirubin 4 ,umol/l (0.2 mg/100 ml) [5-17 ,umol; 0-3-1-0 mg/100 ml], aspartate transaminase 74 U/l