Paget disease of bone is a focal disorder of the skeleton that can affect one or more bones. Many patients are discovered accidentally because of elevated serum alkaline phosphatase activity or an abnormal skeletal radiograph intended to evaluate an unrelated condition. Patients are often asymptomatic, but a subset experience considerable morbidity that can include bone pain and skeletal deformity, as well as a variety of regional complications, such as hearing loss associated with cranial involvement, degenerative arthritis of the hip or knee, fractures of the lower extremities and, rarely, sarcoma or giant cell tumors. Bisphosphonates have proven to be effective in controlling disease activity because they inhibit osteoclast function. Administration of these agents can relieve bone pain, decrease biochemical markers of bone resorption and bone formation, and retard or reverse the early osteolytic phase of the disease. Future studies are needed to determine whether these drugs, if used in an early stage of the disease, can prevent complications in asymptomatic patients.