Primary hyperparathyroidism (PHPT) is not an uncommon endocrine disorder. We describe a patient with PHPT who presented with progressive proximal limbs weakness and dystrophic changes of leg muscles. Serum calcium, alkaline phosphatase, and parathyroid hormone were elevated and serum phosphorus was low. Neck computerized tomography scan showed a parenchymatous tumor in the right lobe of the thyroid. The tumor presented as a 'cold nodule' in the dual-phase single-agent Tc-99m MIBI scan. The right lobectomy examination confirmed the diagnosis of an intrathyroidal parathyroid adenoma of the right gland.