Hemiplegia (or hemiphlegia) is a condition where a vertical half of a patient's body is weak or paralyzed, i.e. one arm and its corresponding leg do not function properly. It can be congenital (occurring before, during, or soon after birth) or acquired (as from illness or stroke). It is usually the result of a stroke, although disease processes affecting the spinal cord and other diseases affecting the hemispheres are equally capable of producing this clinical state.

Cerebral palsy can also affect one hemisphere, resulting in limited function. This does not cause paralysis but instead causes spasms. Cerebral palsy where this is the only symptom is often referred just as hemiplegia.

Hemiplegia is similar to hemiparesis, hemiparesis is considered less severe

Signs of hemiplegia, hemiparesis, or hemiplegic cerebral palsy may include:

• muscle weakness or stiffness - spasticity
• paralysis on one side
• lack of control on the affected side of the body 
• little use of one hand
• limping, toe drop, gait problems
• inproper balancing
• speech or language difficulties
• visual field defects
• seizures (epilepsy)
• perceptual or sensory issues
• specific learning difficulties
• behavioral issues
• IQ scores for children with hemiplegia seem to follow the same range as the general population.