Hereditary patients with a history of treated retinoblastoma (RB) have a greatly increased risk of a broad spectrum of secondary malignancies appearing many years later, with a high incidence in the head and neck region. Leiomyosarcomas (LMS) account for up to 58% of these tumors. LMS in the sinonasal region generally are uncommon and are associated with a locally aggressive course and have a poor prognosis. RB may occur in two forms. The hereditary form is generally bilateral but can present unilaterally with a positive family history and typically exhibits a germline mutation in the RB1 gene on chromosome 13. The non-hereditary form is usually unilateral but can show the same germline mutation in up to 10% of cases. Patients with hereditary RB have been shown to have a significantly higher cumulative risk of developing secondary malignancies than those with the non-hereditary form (28 vs. 1.44% respectively). Most reported cases of sinonasal LMS are in patients with a history of the bilateral hereditary form of treated RB. We report a case of LMS of the nasal sinus area in a 35-year-old African American male with a history of non-hereditary unilateral RB and radiation therapy. To the best of our knowledge, this is the first reported case of sinonasal LMS arising in a patient with a history of non-hereditary unilateral RB. The clinical history, radiology, and pathology are presented along with a brief discussion of the literature. © 2010 Humana.