As monorchidism is rarely reported in horses and no case report has been found in the national literature, the objective was to describe a case in an eight-year old Brazilian adult horse. Using an inguinal approach in the left side, an intact tunica vaginalis was found containing the tail of a malformed epididymis, the ductus deferens and a thin vascular pedicle but without evidence of testicle. Histological and hormonal exams confirmed the absence of testicular tissue. In conclusion, histological and hormonal exams are essential for the diagnosis of monorchidism, which although rare, can also affect national horses
equine; monorchidism; orchiectomy; diagnosis; cryptorchidism
