The present study was performed on Turkish Van cats with tail gland hyperplasia in order to determine changes in some hormone levels and biochemical parameters. Animal material consisted of 18 male Van cats of between 2-8 years of age, 12 with tail gland hyperplasia and 6 unaffected cats as the control group. Following routine clinical examination, hormone levels and biochemical parameters were measured by obtaining blood samples, and biopsy samples were obtained from the region and examined under a light microscope. When compared with the control group, testosterone levels were high although the difference between groups was not statistically significant. Similarly, no statistical significance was found between the groups in terms of other hormones. Among the hormonal parameters, the only remarkable increase was seen in the testosterone level. Among biochemical parameters, the alkaline phosphatase (ALP), aspartate amino transferase (AST), cholesterol and triglyceride levels were statistically different, while other biochemical parameters were not statistically significant. While AST and cholesterol results were increased, ALP and triglyceride levels were decreased. As a result, we conclude that the disease is an important problem which occurs extensively in mature male Van cats, particularly during and after mating periods. We also conclude that the disease might be associated with an increase in testosterone levels. Presenting this study is beneficial as there are limited reports about this disease in cats. This is the first study presenting tail gland hyperplasia with some hormonal levels and biochemical parameters in male Van cats.