The age of crabeater seals Lobodon carcinophagus was first estimated from the teeth by counting layers in the dentine in transverse sections of the canine teeth. Reliable estimation of age from canine teeth in animals older than c. 10 years is not possible because of root closure at a relatively early age. The present investigation compared various methods of estimating age by examination of tooth sections from a large sample of crabeater seals from Marguerite Bay, Antarctic Peninsula. The most reliable estimations were shown to be obtained by counting layers in the cementum of the third postcanine tooth. Ages of 1233 animals (58% female, 42% male) ranged from 0.5 to 39 years. It is suggested that time- and age-specific historical material is potentially relevant for contemporary growth and life-history studies as well as for trophic relations or concentrations of pollutants in animal tissues.