[A case of exostosis based on the left first rib]

Exostosis of the rib is uncommon, especially in the prime of manhood. A 51-year-old man came to our hospital with coin lesion in his left apical region, revealed on routine chest X-ray film. Thoracotomy was done to remove the tumor and the histological diagnosis was exostosis. The tumor, 18 by 18 mm in size, was based on the first rib and grew into the thoracic cavity.