We describe the clinical and genetic findings in pedigree with a novel mutation in the calcium sensing receptor (CaSR) gene and the unusual coexistence of primary hyperparathyroidism (HPT) and familial hypocalciuric hypercalcaemia (FHH) and its clinical management. The occurrence of both FHH and primary HPT in the same patient has been described rarely. Our pedigree has a novel mutation in the CaSR gene. Parathyroidectomy led to a reduction, but not normalization of the calcium levels in the patient identified as having HPT. The coexistence of HPT and FHH was considered in this patient as her calcium and PTH levels were rising with time. Surgical resection of her parathyroid adenoma resulted in reduction of her calcium levels to above normal and significant reduction in her symptoms of fatigue and low mood.