A high variety of factors were found to be implicated in the emergence of depersonalization episodes. The remarkable case of a patient who developed a hemi-depersonalization syndrome is reported in a patient with known obsessive - compulsive disorder. He complained of feeling his left half of the body as if it was detached from him. The part of the body that was perceived as estranged was inconsistent with the anatomical distribution of the nervous system as the entire left part of his body was concerned, from head to toe. He always remained aware that the sensations were not real, and felt like being an outside observer of the left side of his body. He also developed an isolated delusional idea. The hemi-depersonalization syndrome as well as the delusional idea did not respond to citalopram 20 mg/day, but remitted rapidly under olanzapine 10 mg/day, the obsessive - compulsive symptomatology persisting for several weeks. From the course of hemidepersonalization syndrome and the available literature, it is concluded that this syndrome is independent from the concomitant OCD and that the observed hemi-depersonalization syndrome is likely to be a manifestation of a psychotic reaction which consisted of both the hemi-depersonalization and delusions