A person with torticollis has uncontrolled spasms of the muscles in the neck, which result in an abnormally twisted neck position. Some children may be born with torticollis, but the most common cause of torticollis is a drug side effect.

Torticollis usually affects the sternocleidomastoid muscle, a powerful muscle that connects the upper chest to a point on the skull, just behind the ear. Contraction of the sternocleidomastoid muscle causes the head to rotate. Severe contraction and spasm may cause the head to stay rotated and tilted to one side, a condition known as torticollis.