A 56-year-old woman was found to have a solitary mass shadow on chest radiograph in a health examination. Transbronchial examination on two occasions did not yield any diagnostic findings. Both the high level of CA19-9 and the increasingly large shadow were suspected to be indicative of lung cancer, so we performed left lower lobectomy. The pathological examination of the resected lung revealed a granulomatous lesion without malignant findings. A few colonies grew on a liquid medium, and were identified as Mycobacterium avium by PCR. After operation, the increased CA19-9 leval normalized gradually. There are few reports presenting a solitary pulmonary mass shadow and high CA19-9 level due to nontuberculous mycobacterial disease.