Described the eye lens growth of 42 age-known brown hares (Lepus europaeus) by regression models including confidence limits. In addition, lens weights of 369 free-living specimens from the wild were compared with three other indicators of age: "Stroh-sign" i.e. epiphyseal protrusion of the ulna, flexibility of processus lacrimalis and degree of ossification of skull sutures. Due to the slow growth rate and the high individual variability of lens weights in adults estimation of years of age is not possible, but segregating juveniles and adults can be achieved by determination of eye lens weights. Furthermore, within juvenile hares eye lens weights serve for estimation of the date of birth. The "Stroh-sign" appears to be only a crude indicator for separating juveniles from adults. Both the processus lacrimalis and the state of ossification of skull sutures are of no value for a reliable discrimination of juvenile and adult hares.