[en] We report a case of severe dyskinetic syndrome, consisting of intense myoclonia movements, associated with choreiform activity involving the face and upper extremities. The abnormal movements occurred in a patient with confusion and visual hallucinations. This syndrome had an abrupt onset in a patient recovering from coronary artery bypass surgery complicated by an early post-operative cardiac arrest and acute renal failure. Dyskinesia appeared several days after intravenous administration of ranitidine for stress ulcer prophylaxis. Several etiologies were raised in this case among which were post-anoxic myoclonia and metabolic encephalopathy. Cessation of histamine receptor blocker therapy for 48 hours was associated with return of normal cognitive function and disappearance of abnormal movements. This confirmed the iatrogenic nature of the syndrome related to administration of ranitidine.