Carbon monoxide (CO) exposure and toxicity is a potential lethal disorder with immediate and delayed side effects. A 24-y-old driver was admitted to the University-based emergency department with altered mental status. He was found unconscious in the driver's seat of his vehicle in an indoor garage the morning before. An estimated 7 h later, he was comatose and taken to a nearby village clinic. Oxygen was administered immediately. Later, he was transferred to the university hospital. At the 12th h after exposure, the Glasgow Coma Scale score was 12/15 (E3, M5, V4). Co-oximetry disclosed a carboxyhemoglobin concentration of 10.5%. Normobaric oxygen was administered. He recovered completed the 3(rd) d after exposure; however, on the 7(th) d disorientation and agitation was noted, and the interval form of CO poisoning and leukoencephelopaty were suspected, for which he was readmitted the 10(th) d after exposure. Analysis of cerebrospinal fluid and blood revealed no abnormalities. Magnetic resonance imaging on the 11(th) d after exposure demonstrated an ischemic area in the posterior temporoparietal area. The patient continued improvement to discharge at 7(th) d of the second admission. Close follow-up should be scheduled for CO-poisoned patients to rule out the post-interval syndrome for at least 1 mo. This should also include those with apparent clinical and laboratory recovery.