Langerhans cell histiocytosis (LCH) is a rare disease of antigen presenting cells and involvement of thyroid is really uncommon. The thyroid if involved is usually seen in multisystem disease but isolated thyroid involvement is very rare. The diagnosis of Langerhans cell histiocytosis of the thyroid is very challenging due to its rarity and is usually misdiagnosed as benign goiters, undifferentiated carcinoma, lymphoma, etc. Management of Langerhans cell histiocytosis of the thyroid also remains controversial. Prognosis in an isolated Langerhans cell histiocytosis of the thyroid is usually good but as it may precede a multisystem involvement, prolonged follow-up is required. We present a rare case of Langerhans cell histiocytosis of the thyroid, with variable diagnoses on fine needle aspiration cytology.Keywords Thyromegaly . Langerhans cell histiocytosis . Thyroid tumor . Lymphoma thyroid Case StudyA 45-year-old male presented with thyroid swelling for 1 year duration, which was indolent in its course. He had no other complaints. He had no symptoms of hypo or hyperthyroidism. His other medical problems were diabetes mellitus and hypertension. On general examination, the patient was obese, PR-78/min, Bp-160/100 mmHg. Examination of the neck revealed diffusely enlarged, firm thyroid of size 15×8 cm with no nodules. Cervical lymphnodes were not palpable.On investigating, complete hemogram and renal parameters were normal except for elevated blood sugar values for which the patient was started on insulin therapy. Thyroid profile showed normal levels of T3 and T4 with mild elevation of TSH. Antithyroid antibodies were negative. USG of the neck showed goiter with altered echoes. FNAC reports were indecisive, varying between colloid goiter and anaplastic carcinoma. CT of the neck showed diffusely enlarged thyroid with heterogenous attenuation, likely malignant. USG of the abdomen was normal. Both vocal cords were mobile on video-laryngoscopy.The case was discussed in the tumor board and planned for total thyroidectomy for definitive diagnosis. Intraoperatively, the thyroid gland was found to be diffusely enlarged and densely adherent to the strap muscles and trachea. Total thyroidectomy was completed with difficulty after preserving recurrent laryngeal nerves on both sides. The specimen was sent for histopathology (Fig. 1). During immediate postoperative period, patient developed stridor, probably due to tracheomalacia, so he was reintubated. The patient was gradually weaned from ventilatory support and extubated on the 6th postoperative day.Initially, the histopathology of the specimen was reported as non-Hodgkin's lymphoma. With this diagnosis, he was further evaluated for involvement of other sites. CT of the chest, CT of the abdomen, and bone marrow aspiration were