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The ages of polar bears (Ursus maritimus) of known age from 2 to 18 years were estimated through counts of cementum growth layer groups in 105 vestigial, first premolar teeth. Each tooth was read independently by both investigators. The reader with more experience achieved an accuracy of 75% and estimated 93% of the teeth to within 1 year of the correct age. The reader with less experience achieved 58% accuracy and estimated 85% to within 1 year. Accuracy was best in the middle age ranges (i.e., 7-15 years), which are the most critical from a demographic perspective. Our method of determining the age of polar bears represents an almost 2-fold increase in accuracy over methods reported previously. Although our method required more effort and time during processing than standard methods, the higher costs were small relative to the cost of obtaining the samples. Further improvements in accuracy may be possible through the use of standard body-size measurements to identify younger animals and through having the readers with the most experience review teeth that readers with less experience flag as difficult to read.