Benign metastasizing leiomyoma and lymphangioleiomyomatosis (LAM) both are characterized by abnormal proliferation of smooth muscle-like cells in the lung. A 32-year-old African woman with a diagnosis of LAM underwent myomectomy for uterine leiomyomas. An alternative diagnosis of benign metastasizing leiomyoma was made on repeat lung biopsy. Treatment with leuprolide acetate decreased pulmonary infiltrates and improved lung function and exercise tolerance. Accurately diagnosing benign metastasizing leiomyoma has important implications for clinical outcome. Because its clinical presentation may be misleading, immunohistochemical techniques may assist in differentiating benign metastasizing leiomyoma from LAM. This is important because, in benign metastasizing leiomyoma, reduced tumor burden and improved pulmonary function may be achieved by suppressing gonadal steroids.