Gynaecomastia is defined as an enlargement of the male breast with or without pseudolactation. The condition is rarely observed in billy goats and bulls. A billy goat was presented with enlarged teats and thus it was necessary to consider whether it had developed gynaecomastia. Clinical, sonographic, andrological, spermatological, hormone-analytical and histological examinations were performed. The teats were bilaterally enlarged and it was possible to obtain a milk-like fluid. Ultrasonography revealed a parenchyma that looked like mammary tissue. Furthermore, sonographic examination of the testes showed areas of calcification, which is a typical feature of gynaecomastia. The findings were confirmed in the histological examination. A semen analysis provided physiological results. Despite having high levels of testosterone, the male animal did not show any signs of libido. Almost all the findings were suggestive of a true gynaecomastia.