The authors report the case of a young nun who came to their attention because of the simultaneous development of mammary and pelvic lymphoblastic lymphoma and acute leukemia showing aspects typical of nonendemic Burkitt's lymphoma. The rapid tumoral growth and the equally rapid spontaneous cell lysis led to severe renal insufficiency and metabolic acidosis which were ultimately the cause of death. Given the rareness of the clinical situation and the diagnostic problems involved, the authors examined the literature dealing with this subject.