We describe a case of pulmonary capillary hemangiomatosis in a 60-year-old woman with a 1-year history of progressive exertional dyspnea. Four years before admission a diagnosis of breast cancer was made, and she underwent mastectomy plus radiation therapy and treatment with oral antiestrogens. The chest X-ray showed bilateral interstitial infiltrates. Pulmonary function studies revealed a severe restrictive pattern. Abundant red blood cells were found in the bronchoalveolar lavage fluid. On the basis of open lung biopsy, interstitial fibrosis was diagnosed. Cardiac catheterization revealed pulmonary hypertension. Steroids were prescribed, but the patient's condition continued to deteriorate and she died approximately 3 years after presentation. The identification of proliferating and invasive capillaries, which are unique to pulmonary capillary hemangiomatosis, led to the correct diagnosis at autopsy.