Bone marrow transplantation and stem cell transplantation are increasingly used to treat hematologic malignancies and some solid tumors. The treatment entails bone marrow–ablative therapies and intensive medical support to sustain the patient through pancytopenia and other complications of the disease, transplantation process, or drug side effects. Patients who develop graft‐versus‐host disease are the most difficult subset of transplant recipients to manage. Most transplant recipients perform at normal or near‐normal functional levels at the inception of the transplantation process but are at high risk for developing functional deficits as a result of cumulative impairments. These impairments arise from their disease, their prior cancer treatment, transplant induction, graft‐versus‐host disease, immobility, infection, steroid‐related side effects, and other sequelae of transplantation. Preventive and preemptive rehabilitation interventions can minimize functional loss and facilitate recovery, but the transplantation team must be sensitive to and regularly assess for early functional declines in these patients. The physiatrist and the other members of the rehabilitation team must be thoroughly acquainted with the unique needs and challenges of the bone marrow transplantation population in order to design and modify treatment programs effectively and safely. Outcome research has shown that some patients have continued limitations in function despite successful transplantation. Few evidence‐based data are available that addresses factors correlating with poor functional outcomes other than graft‐versus‐host disease. However, this disease has not been investigated utilizing objective functional instruments. Future research should more clearly elucidate the functional impact of allogeneic and autologous transplants by using standardized physical performance measures as well as thorough function‐based symptomatology questionnaires. Cancer 2001;92:998–1007. © 2001 American Cancer Society.