Among the major cancer sites, the lung has the most complicated pTNM description. Reclassification of International Union Against Cancer (UICC)-pTNM grading of 262 lung cancers resected at Shikoku Cancer Center was done using microscopy and audit of pathology reports. Of the 262 lung cancers, 222 were obtained at operation from 1999 to 2004 and 40 additional cases from 2006. Among 666 pTNM components of the former cases, 37 components (31T, 3N, 3M) in 35 cases were revised to different categories. The concordance rate (CR) of the original stage to the reclassified stage was 90% (210/222) in the five-group staging system (5GSS) without subdivisions and 84% (187/222) in the 8GSS with subdivisions such as IA and IB. It decreased in advanced cases. For example, the CR was higher in stage I (97%, 158/163) than in stage II-IV (88%, 51/59) in five-GSS (chi(2) test, P < 0.05). The CR in 8GSS of the additional 40 cases, which were diagnosed after the review of the former 222 cases, was 98% (39/40), indicating that the knowledge gained from the review improved the accuracy significantly (chi(2) test, P < 0.05). It is necessary to assess disparities in the accuracy of pTNM for lung cancer at each institution. This is also true for cancers at other sites.