Topotecan HCl is an antitumor drug exhibiting topoisomerase 1-inhibitory activity. Topotecan is used in the treatment of metastatic carcinoma of the ovary and as second-line treatment of small-cell lung cancer. Reported dose-limiting adverse reactions to topotecan are primarily hematologic in nature. To date, only one other case of lung toxicity in a patient taking topotecan has been reported. The authors describe the development of obliterative bronchiolitis, as evidenced by radiographic and pulmonary function testing abnormalities, in a 61-year-old woman who presented with dyspnea, and who was receiving topotecan for peritoneal carcinomatosis.