Twenty-two cases of resected pulmonary scar cancers in which 10 year or greater follow-up could be obtained were evaluated to determine morphologic and clinical criteria which would predict long-term survival and elucidate the cause and effect relationship of the scar to the cancer. Maturity of the scar was found to be an important criterion in predicting long-term survival. Of patients with tumors less than or equal to 3 cm, only one of six with an early scar died with cancer, whereas four of eight patients with advanced scars died with cancer. All tumors greater than 3 cm had advanced scars and five of eight patients in this category died with cancer. These findings support the concept that the scar develops secondary to the cancer and that the maturity of the scar can be used as a prognostic criterion in resected tumors.