Multiple exostoses is a condition in which people develop multiple abnormal bone growths on the surface of a pre-existing bone. The number and locations of the exostoses varies greatly among individuals with the condition. Affected individuals usually do not have exostoses at birth, but develop them by the time they are around twelve years of age. The growth of exostoses usually stops when an individual reaches physical maturity and the bones stop growing. Multiple exostoses can cause stunted growth, uneven limb lengths, and other skeletal abnormalities. They can often be painful and affect movement. Although exostoses are usually benign, they may become cancerous in some instances. Multiple exostoses may be treated by surgically removing the growths.