TSH-secreting pituitary tumours are very rare and include two opposite clinical conditions: true thyrotroph neoplasia resulting in secondary hyperthyroidism /central hyperthyroidism and pituitary hyperplasia resulting from longstanding primary hypothyroidism. The diagnosis is suspected in patients presenting with headache / biochemical hyperthyroidism high free T4, free T3 and unsuppressed TSH concentrations, particularly in the presence of clinical features of concomitant hypersecretion of other pituitary hormones. However thyrotroph adenomas in long standing hypothyroidism are rare with very few reports on congenital hypothyroidism as primary underlying disease. We present a case of 21 yearr old female who presented with amenorrhoea after removal of contraceptive implant. No symptoms of galactorrhoea. Endocrine investigation: elevated Prolactin 1254 mU/l (102496 mU/l), with normal LH, FSH & oestrodial, TSH >100, Cortisol 430 nmol/l and IGF-1 below normal reference range. Past medical history: congenital hypothyroidism with long standing poor compliance with levothyroxine therapy. MRI pituitary revealed macroadenoma with suprasellar extensions with chiasmatic compression and carotid sinus invasion. Her raised serum prolactin was thought to be related to stalk effect. She started experiencing severe headaches worse on sneezing / coughing. As the adenoma was causing chaismatic compression and she was planning to start family soon, following discussion in the regional pituitary MDT, she underwent transspheniodal surgery. The histology revealed nodular expression of prolactin with evidence of thyrotrope hypertrophy. Postoperatively, MRI pituitary showed no evidence of recurrence of pituitary tumour. This is an extremely unusual case of extreme thyrotropic adenoma requiring surgery. Such thyrotropic adenomas of the pituitary gland are presumed to occur as a result of protracted pituitary stimulation secondary to long-standing thyroid deficiency. Nodular hyperplasia or occasionally a TSH-secreting pituitary tumor can arise in a hyperplastic gland. Future diagnosis and treatment of this rare disorder depend on the recognition of the genetic basis leading to tumor development.