Spontaneous remission of malignant tumors is rare and the biological mechanism of such remission has not been addressed. We report the case of a 71-year-old Japanese patient with non-small cell lung cancer with a right hilar tumor and pleural dissemination that spontaneously regressed. NY-ESO-1 is a cancer/testis antigen that can elicit specific immune responses in patients with cancer. Strong anti-NY-ESO-1 immunity was detected in this patient. His tumor cells expressed NY-ESO-1 and MHC class I molecules. Anti-NY-ESO-1 immunity might have contributed to spontaneous remission in this patient.