The FIV PetCheck ELISA is a practical and commercially available method routinely used for the detection of anti-FIV antibodies in FIV infection. However, false positive and false negative results occur, although the reliability of the negative results is higher than that of the positive results. To determine the predictive value of a positive result in Bavaria, 1911 randomly selected cat sera were collected. Using the PetCheck anti-FIV ELISA, 103 (5.4%) of the 1911 samples tested were positive. These positive samples were reexamined by two other ELISA and by Western Blot. Sixty-one (59.2%) were positive with the second ELISA, 53 (51.5%) with the third ELISA and 40 (40.7%) by Western Blot. Therefore, 59.2% of all positive samples could be considered false positive. The ELISA as a single method to diagnose FIV infection is not reliable in Germany due to the low prevalence of FIV infection. Therefore, a Western Blot confirmation of every positive ELISA is of absolute necessity.