We describe the case of an adult female patient with symptomatic familial hypocalciuric hypercalcemia requiring a step-wise therapeutic approach and the eventual need for a total parathyroidectomy and thyroidectomy to cure symptoms. Genetic analysis demonstrated a heterozygous R227L inactivating CASR gene variant, previously only described in neonatal severe hyperparathyroidism. Post-operative histology showed diffuse hyperplasia of all four parathyroid glands along with the presence of intrathyroidal parathyroid tissue. With regard to clinical management this case suggests that familial hypocalciuric hypercalcemia should be classified as an atypical form of primary hyperparathyroidism rather than a distinct entity.