A 78-year-old asymptomatic woman was referred to our department for the treatment of a right lung tumor. The patient had been suffering from rheumatoid arthritis and followed up in outpatient clinic. On March 6, 1995, abnormal shadow in the right upper lobe was pointed out by routine chest X-ray. Chest CT revealed calcification in the shadow, and benign lesion, such as old pulmonary tuberculosis, was suspected. During follow-up, the size of the shadow and calcification area in the shadow gradually increased. Malignancy was suspected based on the increasing size of the tumor. On July 12, 2000, video-assisted right upper lobectomy with hilar and mediastinal lymph node sampling was performed. Pathological examination revealed that the tumor was primary lung adenocarcinoma containing psamoma bodies in the tumor.