Aim To elucidate the mechanism of occurrence of splanchnic artery aneurysm associated with coeliac artery stenosis due to compression by the median arcuate ligament, and also to discuss the management for this relatively rare condition. Materials and methods Five consecutive cases of splanchnic artery aneurysm associated with coeliac axis stenosis due to compression by the median arcuate ligament, including four cases of pancreaticoduodenal artery aneurysm and one case of epiploic artery aneurysm, were investigated. These cases were collected over a 5-year period in our local and affiliated hospitals. Among these five cases, three were discovered because of rupture of the aneurysm, and two were found incidentally in annual medical check-ups. Results In all cases, conspicuously developed collateral arteries, which were of the dilated pancreaticoduodenal arcade and its branches, were conspicuously found on digital subtraction angiography of the superior mesenteric artery. The findings suggested that haemodynamic changes in the splanchnic arterial networks (an increase in blood flow mainly through the pancreaticoduodenal arcade), were the possible cause of the corresponding aneurysms. Conclusion Compression by the median arcuate ligament might be a frequent cause of splanchnic aneurysm, which, on rupture of the aneurysm, could be life-threatening.