Benign prostatic hyperplasia (BPH) is a very frequent age-related condition in dogs, with 80 percent of intact males over 5 years affected, independently of the breed. Although, castration is a curative treatment for BPH, safe and effective therapeutic medical options are still needed for dogs with high surgery risk, in which castration is not approved by owners or the animal is intended for reproduction. Anastrazole is a drug that has shown to decrease prostatic size in a preliminary study in dogs. The aim of this study will be to test the efficiency and safety of anastrazole upon the treatment of BPH and semen parameters. Twelve male dogs, suffering from BPH, will be treated either with a placebo or anastrazole during 60 days. Prostatic size, clinical, hematological and semen parameters will be assessed monthly before, during and up to 2 months after treatment. Data obtained will be recorded and statistically analyzed. Anastrazole could offer a therapeutic option to medically manage BPH in dogs without affecting fertility.