Human male reproductive disorders comprising testicular dysgenesis syndrome (TDS) have become more prevalent during the last 50 years. These disorders include cryptorchidism, hypospadias, decreased semen quality, and the development of seminomas. Based on experimental evidence, it has been suggested that environmental pollutants with oestrogen-like or anti-androgenic activities play a role in the pathogenesis of TDS. In humans, histological lesions associated with TDS have been well characterized; this includes seminomas as well as their precursors, carcinoma in situ (CIS) lesions. CIS are seminiferous tubules lined by gonocytes and are a sign of testicular maldevelopment. Such CIS have recently been described in canine species, and an increased frequency of testicular tumours in dogs has also been reported. In this study, we investigated the presence of TDS lesions in canine testes submitted to routine histological examination. Histological features considered typical of human TDS were observed in 8/38 dogs examined; as in humans, individual dogs presented with various TDS features with a range of severity. In all eight dogs, CIS and at least one of the histological feature of TDS was observed in combination with seminoma. These findings suggest that as in humans, TDS may predispose canines to develop testicular cancer. A larger study is needed to better evaluate the actual incidence of TDS in canines, its clinical consequences, and the possible underlying pathogenic factors.