Hyperparathyroidism-jaw tumor syndrome is a condition characterized by overactivity of the parathyroid glands (hyperparathyroidism). The four parathyroid glands are located in the neck and secrete a hormone that regulates the body's use of calcium. Hyperparathyroidism disrupts the normal balance of calcium in the blood, which can lead to kidney stones, thinning of the bones (osteoporosis), nausea, vomiting, high blood pressure (hypertension), weakness, and fatigue. About 95 percent of people with hyperparathyroidism-jaw tumor syndrome will develop hyperparathyroidism during their lifetime.~In people with hyperparathyroidism-jaw tumor syndrome, hyperparathyroidism is caused by tumors that form in the parathyroid glands. Typically, only one of the four parathyroid glands is affected, but in some people, tumors are found in more than one gland. The tumors are usually a noncancerous (benign) type of tumor called an adenoma. Approximately 15 percent of people with hyperparathyroidism-jaw tumor syndrome develop a cancerous tumor called parathyroid carcinoma.~People with hyperparathyroidism-jaw tumor syndrome may also have a type of benign tumor called a fibroma in the jaw. Even though jaw tumors are specified in the name of this condition, it is estimated that only 11 to 40 percent of affected individuals have this symptom.~Other tumors, both benign and cancerous, are often seen in people with hyperparathyroidism-jaw tumor syndrome. For example, tumors of the uterus occur in up to 50 percent of people with this condition. Uterine tumors are typically benign, but they can cause heavy menstrual bleeding or other symptoms. The kidneys are affected in about 20 percent of people with hyperparathyroidism-jaw tumor syndrome. Benign kidney cysts are the most common kidney feature, but a rare cancerous tumor called Wilms tumor and other types of kidney tumor have also been found.~Regular medical screening may assist in the early detection of the features of hyperparathyroidism-jaw tumor syndrome.