Unnaturally soft, relaxed, or floppy muscle tone is called hypotonia; muscle tone that is stiff or rigid is called hypertonia. Some infants with CP have hypotonia in the first 2 or 3 months of life and then develop hypertonia. They also might develop an unusual posture or favor one side of the body.

A newborn held on its back and tilted so its legs are above its head will automatically respond with the Moro reflex, extending its arms in a gesture that resembles an embrace. This reflex usually disappears after about 6 months. Infants with cerebral palsy often retain it for an abnormally long period.

Signs of hand preference are also observed. When an object is held in front and to the side, infants usually do not display a tendency to use either the right or left hand. This is normal during the first 12 months of life. Infants with spastic hemiplegia, however, often develop hand preference early, indicating one side of their body is stronger than the other.

The physician will look for other conditions that can be linked to CP, such as seizures, mental impairment, and vision or hearing problems.

Intelligence tests often are administered to a child with CP to evaluate mental impairment, but the results can be misleading and there is a risk of underestimating intelligence. For instance, a child with movement, sensation, or speech problems associated with CP would have difficulty performing well on such tests.