Paraneoplastic pemphigus (PNP) is a refractory and life-threatening autoimmune mucocutaneous disease. We have recently reported the effectiveness and safety of ablative intravenous cyclophosphamide (200 mg/kg daily over 4 days) without stem cell rescue in patients with refractory autoimmune diseases including systemic lupus erythematosus, autoimmune cytopenias, chronic inflammatory demyelinating polyneuropathy, and aplastic anemia. We report chronic lymphocytic leukemia-associated PNP in a patient who presented with extensive and debilitating painful oral ulcerations and received ablative therapy. The patient tolerated the regimen well and showed a slow but sustained improvement despite persistence of the underlying neoplasm. Eighteen months after therapy, the oral ulcerations were almost completely healed and the circulating autoantibodies became negative. Currently, the patient remains on cyclosporine and a low dose of prednisone. This provides further evidence for the efficacy and safety of this regimen in the management of severe autoimmune diseases including PNP. (J Am Acad Dermatol 1999;40:750-4.)