Due to availability of easy routine blood testing, normocalcaemic primary hyperparathyroidism is increasingly seen. However, due to its mild nature, it often poses diagnostic difficulties. We present a case of 65 year old gentleman who was diagnosed with osteoporosis in 2015. He had a history of traumatic fractures of tibia, fibula and calcaneum in 2013. He was later diagnosed with unexplained osteoporosis in 2015 (T-score of hip −2.5 and T-score of spine −1.2) and was treated with alendronate, which was stopped two years later. He was subsequently found to have elevated PTH with normal calcium and phosphate levels (calcium 2.48 mmol/l, PTH 15 pmol/l, vitamin D 121 nmol/l and phosphate of 1.0 mmol/l). His calcium creatinine ratios were 0.0133 and 0.0144. These results were likely to be complicated by previous bisphosphonate therapy. Genetic testing for familial hyperparathyroidism and multiple endocrine neoplasia was negative. His localization studies were negative. Therefore, in order to support the diagnosis of primary hyperparathyroidism, it was decided to proceed with calcium loading test during which he was given one gram of elemental calcium and his PTH, plasma and urinary calcium were measured every hour. His calcium increased from the baseline of 2.45 mmol/l to 2.61 mmol/l which supported the autonomous production of PTH secretion. In view of osteoporosis, he underwent bilateral neck exploration resulting in parathyroidectomy. The histology revealed the parathyroid adenoma and his PTH normalized after surgery. Calcium loading test has been described in the literature for diagnosing normocalcaemic and borderline cases of primary hyperparathyroidism. Although, it is not routinely performed, it can be useful in the diagnosis in such clinical settings.