Leiomyosarcoma is a malignant smooth muscle neoplasm. Patients with treated hereditary retinoblastoma are at a higher risk of a wide range of neoplasms, including leiomyosarcoma. We report here a case of naso-sinusal leiomyosarcoma because of its rarity, and also to highlight the lowest age of its occurrence, as well as the shortest interval between the development of retinoblatoma and naso-sinusal leiomyosarcoma.