A slow, continuous, involuntary writhing movement that prevents maintenance of a stable posture. Athetosis involves continuous smooth movements that appear random and are not composed of recognizable sub-movements or movement fragments. In contrast to chorea, in athetosis, the same regions of the body are repeatedly involved. Athetosis may worsen with attempts at movement of posture, but athetosis can also occur at rest. The phenotype is HP_0002305 (Athetosis). Also known as: Athetoid movements, Involuntary writhing movements, Involuntary writhing movements in fingers, hands, toes, and feet.