Phalanges of adult Bufo bufo were analysed skelettochronologically. The bone appears to reflect the period of metamorphosis as an hematoxylinophilic line, referred to as the line of metamorphosis. If present, it indicates that periosteal bone has not been resorbed in the toads concerned. These specimens formed the basis for estimating the degree of resorption of year rings in the remaining toads. In 82 up to 100% of the toads from the populations studied, the number of year rings resorbed could be estimated. Resorption of year rings appears to stop, once maturity is reached. Interpopulational and intersexual differences were found in resorption, owing to differences in the age at which maturity was reached. Apart from this, the number of year rings resorbed may vary considerably, both individually and among phalanges. Ignoring resorption of year rings in age determination might produce as much as 75% error.