Matsubase town (where our hospital is located) has a history of environmental exposure to asbestos. We reviewed the clinical and radiological features of 8 patients with round atelectasis associated with asbestos exposure who had been examined at our hospital between 1988 and 1997. The subjects were followed up over a period ranging from 6 months to 10 years (mean: 54 months). Round tumors were detected in 6 of the patients by chest CT scans but not by chest X-ray films. Five of those patients underwent transbronchial lung biopsies, and 1 was examined by bronchography. Two patients had a history of pleural effusion. Seven of the patients exhibited round atelectasis in their lower lung fields. The clinical course of round atelectasis was unchanged in all patients. Although round atelectasis is sometimes suspected of being bronchial carcinoma, it can be diagnosed without thoracotomy, on the basis of the patient's medical history and a careful examination of radiological findings.