Care of the medical patient with surgical disease depends on careful evaluation by the surgeon, the anesthesiologist, and the internist. Effective communication and shared information should optimize perioperative management. We have provided a review of anesthetic agents and methods to illustrate expected perioperative changes in physiology that occur with anesthesia. Postoperative complications and side effects of general and regional anesthetic methods have been discussed. With this knowledge the internist can plan for optimal pre-operative medical intervention, provide advice to the anesthesiologist on how anesthesia may affect the patient’s medical condition, and assist in postoperative diagnosis and management of complications.