BACKGROUND Solitary parathyroid adenomas are the leading cause of primary hyperparathyroidism in 0% to 85% of cases. Diagnosis of parathyroid adenoma is based on typical clinical presentation of hypercalcemia, biochemical profile, and modern imaging studies. The purpose of this article is to present the diagnostic and therapeutic approach used for a 73-year-old female patient with a giant parathyroid adenoma measuring 5×2.5×2.5 cm and weighing 30 grams. CASE REPORT A 73-year-old female was referred to the outpatient clinic of our Surgical Department with the diagnosis of primary hyperparathyroidism. The patient suffered from typical symptoms of hypercalcemia such as weakness, bone disease, and recurrent nephrolithiasis; she had a painless cervical mass for 5 months. Primary hyperparathyroidism was confirmed based on the patient's biochemical profile, which showed increased levels of serum calcium and parathyroid hormone. SestaMIBI scintigraphy with 99mTechnetium and cervical ultrasonography revealed a large nodule at the inferior pole of the right lobe of the thyroid gland. Intraoperatively, a giant parathyroid adenoma was found and excised. Additionally, levels of intact parathyroid hormone (IOiPTH) were determined intraoperatively and a 95% reduction was found, 20 minutes after the removal of the adenoma. CONCLUSIONS This is an extremely rare case of a giant solitary parathyroid adenoma. Diagnosis of a giant hyperfunctioning solitary parathyroid adenomas was based on clinical presentation, biochemical profile, and imaging studies. Selective treatment was based on surgical excision combined with IOiPTH levels measurement.