BackgroundLeiomyosarcoma (LMS) is a soft tissue malignant tumor that has a predilection to the abdominopelvic and limb smooth muscles. LMS of the thyroid is exceptionally rare. Papillary thyroid cancer (PTC) is the most common thyroid malignancy and originates from the thyroid epithelial layer. To our knowledge, the presence of both tumors in the same patient has not been reported previously.Case presentation & literature reviewA 42-year-old woman presented with a progressively enlarging neck mass for a few months. She underwent left thyroid lobectomy, and the histology showed high-grade primary LMS of the thyroid. She subsequently underwent a complete thyroidectomy, which identified a classical PTC on her right lobe.Our comprehensive literature review identified 39 published cases of primary LMS of the thyroid. The average tumor size was 5.88 cm and occurred more in women. The most common presentation was neck mass, followed by compressive symptoms. Recurrence and metastasis were uncommon at 15% and 10–25%, respectively.ConclusionThyroid LMS is a rare malignancy with a worse prognosis than PTC. A thorough workup must be done to rule out metastasis before labeling it as primary thyroid cancer.