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The reliability of counting cementum annulations in premolar sections was evaluated for age determination in live polar bears (Ursus maritimus). Structural irregularities in cementum deposits decreased accuracy of age assignments. Displacements of the neonatal line toward the exterior margin of cementum growth resulted in erroneous aging for young animals. Striated, wavered, and doubled growth layers affected accuracy for older animals. Sixty-eight unlabeled tooth slides representing 57 known-age bears, examined by 3 independent investigators, revealed that only 32-45 percent were correctly aged. Analysis of age-related body measurements of 46 male and 63 female polar bears of known age showed that morphometric regression equations could be used as an age indicator. Reproductive status, general body size, and tooth replacement or wear used as criteria to tentatively age animals in the field, combined with subsequent cementum counts and growth regression analyses, provided reliable age determinations.