OBJECTIVE Maffucci's syndrome is a nonhereditary congenital disorder associated with multiple enchondromas, soft tissue hemangiomas, or lymphangiomas. It carries an associated high risk of the development of malignant neoplasms, particularly sarcomatous transformation of an enchondroma, as well as other malignant mesodermal and nonmesodermal neoplasms. Hematopoietic malignancies arising in Maffucci's syndrome are exceedingly rare. We report the case of a 14-year-old girl with Maffucci's syndrome who developed acute lymphoid leukemia. METHODS The patient presented at 18 months of age with enchondromatosis. Maffucci's syndrome was established at 10 years of age after the appearance of multiple hemangiomas. RESULTS At 14 years of age the patient developed fatigue, frequent nosebleeds, easy bruising, and weight loss, with circulating blasts in the peripheral blood. Bone marrow examination showed replacement of marrow spaces with leukemic blasts. Immunohistochemical and flow cytometric findings were consistent with a diagnosis of acute lymphoblastic leukemia with myeloid antigen expression. CONCLUSIONS The occurrence of acute leukemia in a patient with Maffucci's syndrome may represent predisposition to yet another malignancy and reflect further expression of a generalized mesodermal dysplasia in these patients. It also emphasizes the need for aggressive surveillance in patients with Maffucci's syndrome.