Achondroplasia is a rare genetic disorder of bone growth that leads to short stature. Individuals affected with achondroplasia have short limbs, a well-developed trunk, and a head of normal size, except for a protruding forehead.

The condition is caused by a defect of a dominant gene (see genetic disorders) but often arises as a new mutation, rather than being inherited from a parent. The long bones of the arms and legs are affected mainly. The cartilage that links each bone to its epiphysis (the growing area at its tip) is converted to bone too early, preventing further limb growth.

Achondroplasia is usually obvious at birth or during the first year of life and no treatment is available to alter the outlook. Intelligence and sexual development are not affected, and lifespan is close to normal.