Paget's disease is a problem of abnormal bone growth. It may affect just one bone, but it usually affects more than one.

• In normal bone, the bone tissue is constantly being broken down, absorbed into the body, and then rebuilt with new cells.
• In Paget's disease, bone tissue is broken down and absorbed much faster than normal, so the body speeds up the bone rebuilding process. But this new bone is often weak and brittle, and it breaks easily.

Paget's disease is most common in people older than 50, and the risk of getting it increases with age. Most people who have it are able to lead normal lives.