The clinical and pathologic data in 18 patients in whom pneumatosis intestinalis developed after bone marrow transplantation were reviewed to determine the significance of this finding. The colon, predominantly the right side, was involved in 17 of the 18 cases. Pneumatosis intestinalis developed earlier in the 14 symptomatic patients than in the four asymptomatic patients. Symptoms included diarrhea (12 patients), abdominal pain (six patients), rectal bleeding (two patients), and abdominal distension (two patients). Factors contributing to the development of pneumatosis intestinalis included pretransplantation chemotherapy and radiotherapy, steroid therapy, infectious colitis, graft-versus-host disease, and septic shock. Intestinal disease contributed to the deaths of seven patients with pneumatosis intestinalis, necessitated right hemicolectomy in another patient, and resolved with conservative treatment in 10 patients. In summary, bone marrow transplant recipients with pneumatosis intestinalis may follow either a benign or fatal course, depending on the underlying condition of the patient. Clinical correlation is important in determining the significance of this finding.