Populations of European hare (Lepus europaeus) are in decline in Europe, and populations in Australia remain at low densities. Populations are sensitive to size of the breeding stock, which is influenced by fertility in the females. From 1996 to 1999, a total of 272 adult female hares from three Australian populations were dissected and their reproductive systems examined for abnormalities. Cystic endometrial hyperplasia was relatively common and often accompanied by hydrosalpinx. Extrauterine fetuses, neoplasms, pseudopregnancies, and resorptions also were found. However, although pseudopregnancies and resorptions were found in young adults (<12 mo) as well as older hares, conditions possibly causing infertility were almost always in older hares with prevalences up to 46.2%. Only hares with access to known sources of estrogens exhibited pathologic conditions, but sympatric European rabbits (Oryctolagus cuniculus) did not, which is consistent with known difference in responses between the corpora lutea of the two species to exogenous estrogen. Infertility at such a high prevalence could compound and extend the impact of years of low juvenile survival on recruitment.