A 40-month-old child was sedated with a fentanyl and midazolam infusion for 7 days. After the drugs were discontinued he became unresponsive and globally aphasic, and had marked thrombocytosis. He was hospitalized for 4 weeks, during which time his motor and cognitive status slowly improved, and had almost returned to baseline at time of discharge. Severe neurologic abnormalities have been reported with midazolam and fentanyl, administered separately or together, and seem to be a consequence of a withdrawal syndrome. Of interest, this patient had a reactive thrombocytosis at the time of onset of the withdrawal syndrome, and his decreased platelet count coincided with the return to normal cognitive and motor status. Based on this experience and other reports, we believe midazolam-fentanyl combination should be administered with caution.