A 49-year-old male presented with a painful mass in the left scrotum. An inguinal orchiectomy was performed. Pathological examination revealed a well-differentiated leiomyosarcoma completely located inside the testicular parenchyma. We report this unusual case because primary leiomyosarcoma of the testis proper is extremely rare; our patient being the 19th case recorded thus far in the medical literature. It can lead to significant clinical and diagnostic difficulty due to its wide differential diagnosis and extreme rarity.