Patient-controlled analgesia (PCA) is an important means for postoperative analgesia with parenteral opioids. However, postoperative nausea and vomiting (PONV) remains a major complication with a PCA system. Droperidol is used in PCA to prevent PONV. Extrapyramidal reactions by droperidol are, however, occasionally induced. We describe two cases of severe extrapyramidal hypertonic syndrome with an IV administration of droperidol in PCA in two children, following orthopedic surgery. One patient showed a hypertonic syndrome 20 minutes after receiving droperidol 1.0 mg IV and the symptoms persisted for nearly 12 h without prescription. Another patient revealed an acute rigidity 19 h after the beginning of PCA and was treated with an IM administration of midazolam 2 mg successfully.