This report describes an 18-year-old man with disseminated malignant histiocytosis (MH). The patient initially attained complete remission (CR1) with conventional chemotherapy and then relapsed 14 months later. In second complete remission (CR2) 2 years and 8 months after initial diagnosis, an autologous bone marrow transplantation (ABMT) was undertaken following conditioning with the BEAM regimen. Bone marrow collected in CR2 was incubated with mafosfamide at a dose adjusted to the individual sensitivity of normal CFU-GM according to our current protocol. At the time of writing, 4 years post-transplant, this patient remains disease free. This is the first report of ABMT with marrow treated in vitro by mafosfamide in MH.