Abstract Sixty patients (48 women and 12 men), 15 to 86 years of age, with splenic artery aneurysms were studied. Arteriosclerosis, a common histologic finding, was considered a secondary event rather than the initiating cause of most aneuryms. Factors relevant to the pathogenesis of these lesions included: arterial fibrodysplasia affecting eight patients, portal hypertension and splenomegaly in six patients, and inflammatory processes involving the vessel wall in three patients. Among the remaining 43 patients were 35 women, including 14 (40 percent) who had completed six or more pregnancies. Gestational alterations in the arterial wall due to hormonal and local hemodynamic events may have a causal relation to medial defects and aneurysmal formation. Pathogenic factors were less readily identified in eight men who completed the series, although arteriosclerosis was most suspect. Excluding three ruptured aneurysms associated with inflammatory disorders, aneurysmal rupture occurred in only three (5.3 percent) of the other 57 patients. All six patients with ruptured aneurysms survived operation, as did 33 patients with intact aneurysms. Specific risk factors producing aneurysmal expansion and rupture among older, asymptomatic patients are poorly understood. Symptomatic aneurysms and those in women of child-bearing age provide clear indications for operative intervention.