Infiltration of extrahemopoietic tissue with leukemic cells was evaluated as a prognostic indicator in 18 patients with acute leukemia undergoing bone marrow transplantation. When compared to 107 patients who did not have extramedullary leukemia at any time prior to marrow grafting, the patients with leukemic invasion into organs outside the hemopoietic system had a significant increase of leukemic recurrence and a significant decrease in survival after marrow transplantation. Extramedullary leukemia may be a negative prognostic indicator for bone marrow transplantation candidates.