OBJECTIVE The objective of this review is to analyze and describe the use of regional analgesia in the critically ill. DATA SOURCE A Medline search from 1966 to 2004 using the search terms critically ill, nerve blocks, regional analgesia, and regional anesthesia, as well as a search in the Cochrane library, was performed, and standard international textbooks related to critical care and regional anesthesia were searched for practice recommendations. STUDY SELECTION Studies, case reports, and review articles relevant to the topic were included. DATA EXTRACTION AND SYNTHESIS Data were extracted and analyzed in a descriptive fashion. CONCLUSION Regional analgesia using single-injection regional blocks and continuous neuraxial and peripheral catheters can play a valuable role in a multimodal approach to pain management in the critically ill patient to achieve optimum patient comfort and to reduce physiologic and psychological stress. By avoiding high systemic doses of opioids, several complications like withdrawal syndrome, delirium, mental status changes, and gastrointestinal dysfunction can be reduced or minimized. Because of limited patient cooperation during placement and monitoring of continuous regional analgesia, indications for their use must be carefully chosen based on anatomy, clinical features of pain, coagulation status, and logistic circumstances. High-quality nursing care and well-trained physicians are essential prerequisites to use these techniques safely in the critical care environment.