Feline leukemia virus infection is spread globally in the domestic cat population. Together with feline immunodeficiency virus, it is one of the leading infectious causes of death. Like other members of the Retroviridae family, with the help of enzymes reverse transcriptase and integrase, part of the viral ribonucleic acid (RNA) is transcribed into proviral deoxyribonucleic acid (DNA) and is incorporated into the host's genome, which in turn leads to persistent infection in infected individuals. However, even after persistent infection with this virus, different outcomes are possible. Given that there is no effective etiological treatment, and general measures and immunoprophylaxis are the most important ways to prevent the occurrence and spread of this infectious disease, early recognition and determination of the stage of infection is extremely important. The correct choice of diagnostic methods is important because commercial diagnostic tests are not able to detect the infection in its regressive phase, but also because the infected individual is not the source of infection in all stages of the disease. The aim of this study was to evaluate the concordance between serological and molecular methods and assess the need for complementary use of both tests in FeLV diagnosis. For this purpose, a total of 42 feline blood samples were analyzed using serological and molecular diagnostic methods. The infection was confirmed in 15 samples using a serological diagnostic method, i.e. a commercial immunoenzyme test, while the findings were negative in the remaining 27 samples. The molecular diagnostic method confirmed the presence of the provirus in all 15 serologically positive samples, therefore the concordance between the positive serological test and the molecular diagnostic method was 100%. Among 27 serologically negative samples, FeLV infection was detected in two additional samples by proviral PCR. In this case, the agreement between a negative serological finding and the molecular method was 92.6 %. Our results confirm the necessity of using both diagnostic methods to establish a reliable and accurate diagnosis. Complementary application is also important to determine the stage of the infection, which is extremely important for effective control of FeLV infection.