FeLV infection exists worldwide and is among the most common infectious diseases of cats, which has an important impact on the health and lifespan of domestic cats. The virus belongs to the Retroviridae family and like other members of this family, it is associated with lifelong infection after integration of the proviral DNA into the host cell genome. Cats usually get infected through the saliva from the cat which is already infected with FeLV. Cats with a progressive infection become persistently viremic and they are contagious to other cats for the rest of their lives, they live shorter, on average no more than 3 years from getting diagnosed and sooner or later they will develop clinical signs associated with FeLV infection (neoplasia, hematopoietic disorders, neurologic disorders, immunodeficiency, immune-mediated diseases and stomatitis). FeLV infection is associated with a variety of clinicopathologic abnormalities, those cats often have concurrent bacterial, viral, protozoal, and/or fungal infections including feline upper respiratory tract disease (FURTD). Hematopoietic disorders associated with FeLV infection include anaemia, neutropenia, thrombocytopenia and pancytopenia. The most clinically important consequence of retrovirus infections is immunosuppression. It is important to understand that many secondary diseases in FeLV-infected cats are treatable. Preventing exposure of healthy cats to FeLV-infected cats by test and removal or isolation is an important key to preventing the spread of the disease. The initial test for diagnosis of FeLV relies on the detection of the core antigen p27 in peripheral blood using an enzyme-linked immunosorbent assay (ELISA). When ELISA is used for screening testing, confirmatory testing for cats with positive or suspiciously (slightly positive) test results is strongly recommended. Except for ELISA, it can be also used as IFA and PCR. A confirmed positive FeLV antigen test result should never be a death sentence for a cat if circumstances allow keeping the cat separated from other cats. Antiviral and immunomodulatory medicines are used in the treatment of FeLVinfected cats, as well as symptomatic and supportive therapy. The most important and efficient measures of controlling FeLV are testing, identification and separation of infected cats to prevent the exposure of healthy cats to the virus and the spread of the infection, vaccination is also an important preventive tool.