A system is described for estimating the age of the African lion by studying the eruption sequence of deciduous and permanent teeth of both jaws and the wear of permanent teeth. This system is supplemented by observing criteria such as height of the cemento-enamel line of permanent canines above the alveolar margin, the closure of the apical foramen of the pulp chamber and the discolouration of permanent teeth. Where skulls are available curves and equations describing closure rate with age of the pulp chambers of maxillary and mandibular canines measured at their maximum mesio-distal width, are provided. These measurements can be taken by either sectioning the canines transversely at a certain point or by X-raying the teeth. Sex-specific von Bertalanffy growth curves and equations describing skull growth with age for four skull measurements are also provided while the use of cranial sutures for age determination in the lion is evaluated. Canine root sections were removed, decalcified, sectioned and stained for incremental cementum line counts. The results of this method were in close agreement with the ages of known-age lions and those aged by the previously mentioned methods (r=0.973; P<0–001). A series of photographs and a description is provided whereby lions observed in the field can be classified into age classes. Sexual dimorphism in the permanent canines is described and appropriate measurements given whereby a single permanent canine can be used to decide on the sex of an animal. The use of oxytetracycline and lead acetate for the in vivo“labelling” of teeth in wild lions is examined.