Thyrolipomatosis, a diffuse non-neoplastic infiltration of fatty tissue in the thyroid gland, is an extremely rare condition with only about 30 cases reported worldwide. A few of these cases report the concurrency of thyrolipomatosis and malignant neoplasms in the thyroid or colon, but never with tongue cancer. A 44-year-old female patient with an infiltrative tongue mass suggestive of carcinoma presented for an outpatient consultation. Cervical imaging revealed multiple lymphadenopathies and a multinodular goitre with diffuse fatty infiltration, suggestive of thyrolipomatosis. Surgical intervention included partial resection of the tongue and thyroid (left hemiglossectomy and right hemithyroidectomy, respectively) and lymphadenectomy. The thyroid specimen showed diffuse fat metaplasia of the stromal thyroid tissue, confirming incidental thyrolipomatosis. During post-operative follow-up, the patient presented with recurrence of squamous cell carcinoma as indicated by new right-sided thyroid nodules, left-sided lymphadenopathies with confirmatory biopsy, and a growing neck mass that became infected. The patient developed septic shock and later died. Thyrolipomatosis causes thyroid swelling and can be clinically detected as goitres or as an incidental finding. Diagnosis is suggested by cervical imaging (ultrasonography, computed tomography or magnetic resonance), but confirmation is histological after thyroidectomy. Although thyrolipomatosis is benign, it could develop concurrently with neoplastic diseases, especially on embryologically related tissues (e.g. thyroid and tongue). This case report is the first in the literature describing the coexistence between thyrolipomatosis and tongue cancer in an adult Peruvian patient.