Retrospective computer analysis of all reportable cases of thyroid cancer for the Rocky Mountain Cancer Data Systems between 1973 and 1983 was undertaken. Follow-up data were available for periods of 5 to 10 years. All major histologic findings are reviewed with regard to distribution, prognostic factors, mortality rates, and some treatment modalities. Interesting observations determined by this study include: (1) the significantly greater mortality rates seen in patients with thyroid cancer after 50 years; (2) the lack of increased mortality rates in young patients with differentiated cancer; (3) the poorer prognosis of male patients of equivalent age to female patients in all histologic types of cancer in the first 5 years; (4) the lack of sexual difference in influencing mortality rates after the first 5 years in differentiated cancers and lack of sex as a prognostic indicator in undifferentiated cancers; (5) the excellent prognosis of patients with localized differentiated and medullary cancers and a better-than-expected prognosis in the undifferentiated group; (6) the clear need for combined therapy (surgery and irradiation) in regional medullary cancer; (7) the observation that localized thyroid lymphoma had a higher mortality rate than had regional thyroid lymphoma; and (8) a significantly higher mortality rate in patients older than 79 years with differentiated cancer.