Usage of the term "alien hand sign" is reviewed in 20 published cases. It refers to apparently purposeful, upper-extremity movements that the patient reports are beyond his/her control. Lesions were found in medial frontal cortex and/or the corpus callosum with presentation being unilateral and transient, unless bilateral cortical and subcortical structures were involved. There was a high co-occurrence of speech hesitation, limb dyspraxia, tactile dysnomia, muscle weakness, and grasp reflex on the alien side. Five behavioral manifestations of alien movement have been described, with grasping movements and intermanual conflict being the most common. Two manifestations, exaggerated ataxic automatisms and drifting movements, likely represent other types of movement disorders. Dysfunction of the supplementary motor area and related structures has been implicated, but the exact causal mechanism remains uncertain.