Cerebral palsy (CP) is a group of movement disorders that appear in early childhood. Signs and symptoms vary among people and over time, but include poor coordination, stiff muscles, weak muscles, and tremors. There may be problems with sensation, vision, hearing, and speech. Often, babies with cerebral palsy do not roll over, sit, crawl or walk as early as other children. Other symptoms may include seizures and problems with thinking or reasoning. While symptoms may get more noticeable over the first years of life, underlying problems do not worsen over time.

Cerebral palsy is caused by abnormal development or damage to the parts of the brain that control movement, balance, and posture. Most often, the problems occur during pregnancy, but may occur during childbirth or shortly afterwards. Often, the cause is unknown. Risk factors include preterm birth, being a twin, certain infections or exposure to methylmercury during pregnancy, a difficult delivery, and head trauma during the first few years of life. A study published in 2024 suggests that inherited genetic causes play a role in 25% of cases, where formerly it was believed that 2% of cases were genetically determined.

Sub-types are classified, based on the specific problems present. For example, those with stiff muscles have spastic cerebral palsy, poor coordination in locomotion have ataxic cerebral palsy, and writhing movements have dyskinetic cerebral palsy. Diagnosis is based on the child's development. Blood tests and medical imaging may be used to rule out other possible causes.

Some causes of CP are preventable through immunization of the mother, and efforts to prevent head injuries in children such as improved safety. There is no known cure for CP, but supportive treatments, medication and surgery may help individuals. This may include physical therapy, occupational therapy and speech therapy. Mouse NGF has been shown to improve outcomes and has been available in China since 2003. Medications such as diazepam, baclofen and botulinum toxin may help relax stiff muscles. Surgery may include lengthening muscles and cutting overly active nerves. Often, external braces and Lycra splints and other assistive technology are helpful with mobility. Some affected children can achieve near normal adult lives with appropriate treatment. While alternative medicines are frequently used, there is no evidence to support their use. Potential treatments are being examined, including stem cell therapy. However, more research is required to determine if it is effective and safe.

Cerebral palsy is the most common movement disorder in children, occurring in about 2.1 per 1,000 live births. It has been documented throughout history, with the first known descriptions occurring in the work of Hippocrates in the 5th century BCE. Extensive study began in the 19th century by William John Little, after whom spastic diplegia was called "Little's disease". William Osler named it "cerebral palsy" from the German zerebrale Kinderlähmung (cerebral child-paralysis). Historical literature and artistic representations referencing symptoms of cerebral palsy indicate that the condition was recognized in antiquity, characterizing it as an "old disease".

Cerebral palsy is defined as "a group of permanent disorders of the development of movement and posture, causing activity limitation, that are attributed to non-progressive disturbances that occurred in the developing fetal or infant brain." While movement problems are the central feature of CP, difficulties with thinking, learning, feeling, communication and behavior often co-occur, with 28% having epilepsy, 58% having difficulties with communication, at least 42% having problems with their vision, and 23–56% having learning disabilities. Muscle contractions in people with cerebral palsy-related high muscle tone are commonly thought to arise from overactivation. Although most people with CP have problems with increased muscle tone, some have low muscle tone instead. High muscle tone can either be due to spasticity or dystonia.

Cerebral palsy is characterized by abnormal muscle tone, reflexes, or motor development and coordination. The neurological lesion is primary and permanent while orthopedic manifestations are secondary to high muscle tone and progressive. In cerebral palsy with high muscle tone, unequal growth between muscle-tendon units and bone eventually leads to bone and joint deformities. At first, deformities are dynamic. Over time, deformities tend to become static, and joint contractures develop. Deformities in general and static deformities in specific (joint contractures) cause increasing gait difficulties in the form of tip-toeing gait, due to tightness of the Achilles tendon, and scissoring gait, due to tightness of the hip adductors. These gait patterns are among the most common gait abnormalities in children with cerebral palsy. However, orthopaedic manifestations of cerebral palsy are diverse. Additionally, crouch gait (also described as knee flexion gait) is prevalent among children who possess the ability to walk. The effects of cerebral palsy fall on a continuum of motor dysfunction, which may range from slight clumsiness at the mild end of the spectrum to impairments so severe that they render coordinated movement virtually impossible at the other end of the spectrum.

Babies born with severe cerebral palsy often have irregular posture; their bodies may be either very floppy or very stiff. Birth defects, such as spinal curvature, a small jawbone, or a small head sometimes occur along with CP. Symptoms may appear or change as a child gets older. Babies born with cerebral palsy do not immediately present with symptoms. Classically, CP becomes evident when the baby reaches the developmental stage at 6 to 9 months and is starting to mobilise, where preferential use of limbs, asymmetry, or gross motor developmental delay is seen.