Parathyroid glands produce parathyroid hormone (PTH), which regulates serum calcium levels and bone metabolism. Typically, four glands are located behind the thyroid. Overactive glands, often benign adenomas, secrete excessive PTH, causing hypercalcemia. This stimulates calcium absorption and bone resorption, leading to symptoms like fatigue, weakness, depression, and constipation, along with high serum calcium, elevated PTH, and low phosphorus. Conversely, hypoparathyroidism results from insufficient PTH production, often due to thyroid surgery. This causes hypocalcemia, leading to symptoms such as tingling, muscle cramps, and cardiac arrhythmias, along with low serum calcium and high phosphorus. Treatment for hypoparathyroidism involves activated vitamin D, calcium supplements, or injectable PTH. Rare parathyroid carcinomas can also lead to challenging cases of hyperparathyroidism.