Polyorchidism is an uncommon congenital anomaly. We systematically analyzed the literature due to the contradictory data regarding this condition.We conducted a database search and evaluated relevant articles for the appearance, comorbidities and complications of supernumerary testes. Only cases of polyorchidism confirmed by histological examination were included in the study.We found 140 cases of polyorchidism. Triorchidism was the most common type, and 6 cases of 4 testes (4.3%) were reported. Most supernumerary testes (64%, chi-square p <0.001) were drained by a vas deferens. Median patient age at detection was 17 years. Left side demonstrated predominance (64.5%, chi-square p <0.001). Most cases were found during surgery for other symptoms including inguinal hernia, undescended testicle, testicular torsion and scrotal pain. Only 16% of patients complained of an accessory mass without any symptoms. Neoplasms were found in 9 cases (6.4%), of which 8 were malignant and 1 was benign. Data available for 7 malignomas (88%) revealed that all were in cryptorchid supernumerary testes.Polyorchidism is rare and is generally found during evaluation for other conditions such as inguinal hernia, undescended testis and testicular torsion. Cryptorchidism appears to be the most important risk factor for malignancy in patients with supernumerary testes. Thus, patients with nonscrotal supernumerary testes require appropriate counseling. The supernumerary testis is frequently drained by a vas deferens, implying a probable reproductive function. Decision for surgery, biopsy or orchiectomy should be based on concomitant symptoms, cryptorchidism or suspected malignancy. We provide a guideline for management based on a functional classification of polyorchidism.