Secondary hyperparathyroidism results from excessive production of PTH due to persistently low serum calcium level due to any cause including Vit. D deficiency, lack of calcium intake, ch. renal failure, Vit. D resistant rickets and renal tubular dysfunction. Ch. renal failure is the most common cause of secondary hyperparathyroidism in paediatric age group. Persistently low levels of calcium stimulate parathyroid glands to secrete PTH in excess which causes resorption of the bones in addition to increasing absorption of calcium from the gut. Bones become soft, fragile and prone to pathological fractures.