Multinucleated giant cells (MGCs) are produced by the fusion of white blood cells. Each resultant MGC suggests a specific condition and may even signify associated diseases. These cells are problematic when associated with osteoporosis, arthritis, and implant rejection. Some of the important multinucleated giant cells are explained below. Osteoclasts are cells that dissolve bone. They are very active in normal bone growth phases, where they give proper shape to the bone along with osteoblasts, which are the bone forming cells. Osteoclasts are responsible for bone degradation and the subsequent reduction of bone density. These cells are very active in diseases that cause reduced bone density. Foreign body giant cells (FBGC) are found at foreign body sites including stitches and various implants such as oral, breast and bone implants. Furthermore, these giant cells form around organ transplant sites and in some pathological diseases including tumours.