THREE recent reviews1,2,3have stressed the unilaterality of benign mesenchymomas of the kidney (hamartomatous angiomyolipoma) except in those patients with tuberous sclerosis. The sudden onset of shock is reported by Price and Mostofi3in two of 30 patients and is even more of a rarity in the sporadic cases reported in the English language literature.1-31The following report demonstrates both that this lesion can be bilateral and that severe spontaneous retroperitoneal hemorrhage can rapidly develop. Report of a Case A 42-year-old white woman (JMCH 217456) with no evidence of tuberous sclerosis was in good health until June 22, 1962, when severe right flank, abdominal and back pain developed and she was admitted to Delaware County Memorial Hospital. Despite no obvious external blood loss hypovolemic shock developed necessitating blood replacement. Abdominal x-ray film showed absence of the right psoas shadow, and an intravenous pyelogram revealed no calyceal deformity