Abdominal aortic aneurysms are rare in children. Causes include mycotic aneurysms, vasculitides (eg, Takayasu's arteritis), connective tissue diseases (eg, Marfan's syndrome, Ehlers-Danlos syndrome, and tuberous sclerosis) and traumatic false aneurysms. Four cases are described. Case 1 was a 12-year-old boy who presented with an acute unheralded rupture of the subdiaphragmatic aorta accompanied by lower limb paralysis and ischemia. Attempted repair failed because of extensive friability of the large arteries. Histological evaluation confirmed cystic medial necrosis despite Marfanoid phenotype. Cases 2 and 3 were boys aged 12 and 11 with Takayasu's arteritis who presented with hypertensive encephalopathy and heart failure. Although both had involvement of the origins of the renal arteries, one aneurysm was predominantly suprarenal and the other infrarenal. Currently both children are being managed successfully with antihypertensive therapy. Case 4 was a 5-year-old girl who presented with hypertension and a pulsatile abdominal mass after treatment of infective endocarditis 18 months previously. Arteriography and three-dimensional computed tomography confirmed an aneurysm (6 x 5 x 4 cm) arising from the aorta and involving the right renal artery. Aneurysmectomy, removal of a small ischemic right kidney, and Gore-Tex grafting resulted in cure of the hypertension and uneventful recovery. The present series confirms that rupture is a fatal complication, renovascular complications are common, and medical control of hypertension is an essential part of management. Management strategies need to be highly individualized, and may be successful without surgical intervention. Close clinical and ultrasound follow-up of those managed nonoperatively is essential.