Summary:A 46-year-old woman developed concurrent CMV and Pneumocystis carinii pneumonia (PCP) 140 days after autologous peripheral blood stem cell transplantation (APBSCT) for AML. She was seropositive for CMV before undergoing APBSCT and had required prednisone for immune thrombocytopenia and allergic dermatitis for 9 weeks prior to the onset of pneumonia. She had also been receiving PCP prophylaxis with pentamidine aerosol every month for 3 months before developing symptoms. The pneumonia was complicated by severe hypoxia, requiring ventilator support and pneumothorax requiring chest tube thoracostomy. She recovered following treatment with trimethoprim-sulfamethoxazole (TMP-SMX), prednisone, gancyclovir and intravenous immunoglobulin. Although the overall incidence of severe CMV disease is low after APBSCT, preventive measures such as surveillance culture and secondary prophylaxis with gancyclovir may be warranted in patients whose cellular immune response is further compromised by corticosteroid use or other factors.