A 72-year-old woman was admitted to our hospital with a solitary right lung nodule. She had no symptoms and no abnormal physical findings except for bladder cancer. Tumor markers were mildly elevated but no other abnormal laboratory data were found. The nodule was diagnosed to be pulmonary mucosa-associated lymphoid tissue lymphoma on computed tomography-guided needle biopsy. Thereafter, she first underwent surgery for bladder cancer. The lung nodule was found to have slightly increased at three months and then disappeared at 15 months after the biopsy. The notable clinical course of this rare disease suggests the effectiveness of a non-interventional treatment strategy.