Objectives: To report a case of signet ring cell adenoma of the thyroid which is an extremely rare thyroid lesion. Clinical Presentation and Intervention: A 25-year-old female patient presented with a goiter and dysphagia that had been present for the last 1 year before admission. Physical examination revealed a palpable solitary nodule in the right lobe of the thyroid. The ultrasonogram demonstrated multiple nodules among which the most remarkable one was 15 × 24 mm in size, in the right lobe of the thyroid. After surgical excision, the lesion was found to be consistent withsignet ring cell adenomacharacterized by the presence of round to oval signet ring cells with large cytoplasmic vacuoles and hyperchromatic eccentric nuclei. Intracytoplasmic thyroglobulin, periodic acid-Schiff (PAS) with and without diastase and combined Alcian-blue-PAS were all positive. Conclusions: Pathologists should keep this rare primary tumor of the thyroid in mind when examining thyroid lesions and should not confound it with metastatic signet ring cell carcinoma of the thyroid.