Benign Prostatic Hyperplasia (BPH) is a common disease of non-castrated dogs, with a high prevalence (>80%) in dogs over 5 years. The use of anti-androgens represents an interesting alternative to surgery. A multicentric, controlled and randomised clinical field trial was conducted in 4 European countries to evaluate the efficacy of Osaterone acetate (OSA) tablets on dogs presenting with clinical signs of BPH. OSA tablets administered at a dose of 0.25 mg/kg bw once daily for 7 days were compared to delmadinone acetate (Tardak®, Pfizer) administered once IM or SC at a dose of 3 mg/kg bw. Over a 6-month follow-up period, the dogs were examined on 5 different time points: D0, D14, D60, D120 and D180. At each visit, a clinical examination was performed and the size of the prostate was determined by ultrasonography. Efficacy of the products was assessed by the percent reduction of the prostate size and the clinical recovery rate (complete resolution of clinical signs) on D14. Product persistence of activity was estimated from the average time to requirement of a second course of treatment. One-hundred forty-two dogs of various breeds were included in the study: 73 were treated with OSA and 69 with Tardak. On D14, the prostate volume was reduced by 38% with OSA and 27.6% with Tardak (p=0.002). Clinical recovery was reported in 36 dogs (49.3%) in the OSA group and 33 (47.8%) in the Tardak group (p=0.8592). Over the whole 6-month period, a clinical score of 0 was achieved in 92% of dogs treated with OSA. OSA persistence of activity was at least 161 days, an intermediate estimation to be re-evaluated after additional long term follow-up of the dogs. Tolerance to OSA was good, a slight increase in appetite was sometimes recorded and managed with appropriate food intake monitoring. A short 7-day course of Osaterone acetate tablets proved an efficient, long-lasting and safe therapeutic regimen for Benign Prostatic Hyperplasia in dogs.