Splanchnic artery aneurysms were encountered in 45 patients. This experience and a comprehensive review of the literature since 1960 resulted in revision of many preexisting concepts concerning the pathogenesis and prognostic implications of these lesions. Most significant is that multiparity may result in medial degeneration with subsequent development of splenic artery aneurysms. A previously unrecognized association of renal artery fibromuscular disease and splenic artery aneurysms was documented. The established morbidity and mortality attributed to all aneurysms of the splanchnic arteries justifies prompt surgical treatment once their presence is known.