This is the third in a series of articles relating results from a line of research whose intent was to construct a complete history of patient interactions with the health care system using available data sources for all patients diagnosed in 1990 with a primary breast, colorectal, or lung tumour in Manitoba. This article presents details of the development and application of methods to produce TNM staging data on the roughly 2,000 patients in this population. The operational definitions constructed for this research can be adapted for other tumour sites and data sources. Findings include methods developed to overcome the sometimes ambiguous and inconsistent available documentation, which ultimately produced reliable TNM staging data. Survival data for this population by stage of disease are given.