Dexmedetomidine (DEX) is widely used in intensive care unit for perioperative sedation. The one advantage of DEX administration for sedation is the lack of significant respiratory depression. However, DEX shows significant interaction with anesthetics and narcotics, and we present a case in which post-anesthetic administration of DEX induced apnea and severe respiratory depression after extubation. A 74-year-old, 38.3 kg, 148 cm woman was scheduled to undergo implantation of internal cardiac defibrillator. General anesthesia was maintained by sevoflurane, remifentanil and intermittent administration of fentanyl. After the surgery, she was transferred to intensive care unit with intubation, and DEX administration was commenced. After 3.5 hr from the end of anesthesia, the patient's trachea was extubated under continuous infusion of DEX (0.26 microg x kg(-1) x hr(-1)). Ninety min later, she showed apnea and severe respiratory depression. The interaction of DEX and residual narcotics might have induced life-threatening respiratory complication.