Hemiplegia (sometimes called hemiparesis) is a condition that affects one side of the body (Greek 'hemi' = half). It is caused by injury to parts of the brain that control movements of the limbs, body, face, etc.

This injury may happen before, during or soon after birth (up to two years of age approximately), when it is known as congenital hemiplegia (or unilateral cerebral palsy). If this happens later in life as a result of injury or illness, it is called acquired hemiplegia. We also talk about a right or left hemiplegia, depending on the side affected. Generally, injury to the left side of the brain will cause a right hemiplegia and injury to the right side a left hemiplegia.

Hemiplegia is a relatively rare condition, affecting up to one child in 1,000. About 80% of cases are congenital, and 20% acquired. Hemiplegia affects each child differently.

You may be told that hemiplegia is a form of cerebral palsy, which is a descriptive name for a wider group of conditions in which movement and posture are affected owing to injury to the brain. These conditions are lifelong and non-progressive, which means they do not get worse. They may look different over time, partly because the child is growing and developing.