Context: Primary hyperparathyroidism (PHPT) is commonly associated with reduced bone mineral density (BMD) presenting with osteoporosis, increasing the risk of bone fragility fractures in these patients. Bisphosphonates, due to their anti-resorptive action, are known to improve the BMD and reduce the risk of bone fragility fractures. Therefore, bisphosphonates are considered as an alternative to surgical treatment in managing osteoporosis in PHPT patients. Aim: The aim of this observational study was to assess the effect of long term bisphosphonate therapy on BMD, bone fragility fracture and biochemical markers of bone metabolism in patients with PHPT. Methodology: Fifty patients (mean age 74 years) with PHPT who were treated with long term bisphosphonate therapy were studied retrospectively. The mean baseline (before commencing bisphosphonate therapy) BMD T-scores for lumbar spine (L2-L4) and left femoral neck were -2.5 and -2.1, respectively. Fourteen patients had bone fragility fractures before initiation of bisphosphonate therapy. Results: After an average of 5 years of bisphosphonate treatment, there was a significant increase in lumbar BMD T-score (-2.5 to -2.1, p = 0.013) and a non-significant change in left femoral neck BMD T-score (-2.1 to -2.2, p = 0.497). There was no increase in bone fragility fracture rate (p = 0.167). Serum corrected calcium reduced from 2.74 mmol/L to 2.60 mmol/L (p < 0.001) and urine calcium to creatinine ratio from 0.70 to 0.55 (p < 0.0001), both within the reference range. Conclusions: Our study suggests that long term bisphosphonate therapy improves lumbar BMD and prevents increase in bone fragility fracture rate. Additionally it improves hypercalcaemia in PHPT.