Thornyhead rockfishes (Sebastolobus altivelis and S. alascanus have been commercially harvested at an increasing rate off the west coast of the United States. Age estimates from otoliths indicate that both species are long-lived, potentially making the populations vulnerable to heavy fishing pressure. The purpose of this study was to verify longevity by quantitatively comparing growth patterns in otoliths with the radiochemical age of their cores. Growth increment patterns visible in transverse otolith sections from these two species were narrow, often irregular, and difficult to interpret, resulting in poor ageing precision. A technique that measures the radiochemical disequilibria between natural 210Pb and 226Ra in otolith cores was used to independently determine longevity. Levels of 210Pb:226Ra disequilibria in otolith cores confirmed ages of at least 45 years for S. altivelis and 80 years for S. alascanus. This technique, however, is very sensitive to small variation or errors in 226Ra measurements when 210Pb levels reach approximately 75% of the equilibrium value. Ages over 80 years, estimated for S. alascanus, could not be confirmed due to variation in 226Ra assays.