<prompt> The commonest cause of primary hyperparathyroidism is :Carcinoma parathyroidSolitary adenoma of parathyroidChronic renal failureHyperplasia of the parathyroid  <response>: Ans. is b Parathyroid adenoma Ref Harrison, 17e, p 2380 16e, p 2252 15e, p 2210.Most common cause of primary hyperparathyroidism is parathyroid adenoma. 