A case of bone marrow necrosis (BMN) in transplanted acute lymphoblastic leukaemia (ALL) is presented. The propositus is a 16 year-old boy with L-2 type ALL on whom allogeneic bone marrow transplantation (BMT) had been performed after the second relapse. He was admitted to hospital at 415 after BMT with fever, malaise and hip pain. One week later he had aplasia without blast cells. Scanty cellularity with necrobiosis was found in bone marrow aspirates; bone marrow biopsy confirmed the suspicion of BMN. Osseus scintigraphy with 99-Tc-diphosphonate showed poor, irregular distribution. Steroid therapy was followed by a favourable response. Peripheral blast cells appeared two weeks later, and the relapse was confirmed by bone marrow aspiration. Chemotherapy was started, but the patient died on day 467 after BMT. BMN has been reported in ALL at onset, in relapses, after chemotherapy and as necropsy finding; however, it had not been found in patients subjected to BMT. The experience of these Service was revised, this being the only case of 140 patients subjected to BMT who presented such severe complication.