Survival and prognostic factors were studied in 2479 clinically presenting thyroid cancers (TC) reported from the entire Norwegian population from 1970 to 1985. Complete follow-up was obtained (median, 48 months), with information on causes of death. At the end of the observation period, 498 patients were reported to have died of TC, representing 69.7% of all deaths. Among 216 patients dying of other main causes, TC was considered to be a contributing cause of death in 80 cases (11.2%). Multivariate regression analysis of TC deaths showed no significant difference according to sex in any of the histological types. Age had a strong impact on survival, and for papillary carcinomas this effect was apparent after the age of 55 years. Marked differences were observed between various histological types, even between papillary and follicular carcinomas when interactions were included. Furthermore, tumor stage was a strong predictor of TC deaths, and a reduced survival was also found in patients with lymph node metastases. In conclusion, the importance of age, histological type, and tumor stage as major prognostic factors has been documented in this population-based study from Norway.