Psychomotor performances are frequently impaired in patients with cerebral lesion. The locus of lesion seems to play an important role: patients with right hemispheric lesion (RHL) frequently show a more important impairment in reaction to external stimuli than patients with left hemispheric lesion (LRH). The aim of this work was to study simple and choice visual reaction times in 2 groups of hemiplegic patients, with different hemispheric lesion side. Results confirm that patients with RHL have significantly more prolonged reaction times. No differences were found in a time we called choice time, related to "central delay" confirming that the more important psychomotor performances deficit in RHL patients is mainly related to impairment of attention, alertness, arousal systems.