Scrotal masses, especially tumors, are fairly common in intact older male dogs. Testicular tumors have an approximately 7% to 16% incidence rate (the number of new cases per population in a given time period) and a mean age of 10 years old at the time of being discovered. Of these testicular tumors, the 3 most common types are Sertoli cell tumors, seminomas, and Leydig cell tumors. Sertoli cell tumors account for 19% of these testicular in intact dogs; seminomas 23%, and Leydig cell tumors/interstitial cell tumors 58%. Some studies have indicated that cryptorchidism has a higher predisposition to cause Sertoli cell tumors. The general agreement is that a successful castration will eliminate the risk of developing testicular cancer. Sometimes this is not the case, as there have been reported accounts of successful castration in canines who then develop a tumor of testicular cell type with no evidence of testicular tissue remnants. This paper looks in depth at a case of an older canine that was castrated at a young age but then developed a testicular cell tumor.