Multiple aspects of perianesthesia care and the perioperative environment can influence the functions of the immune system. This course reviews basic immune system functions and potential sources of immune system-altering perioperative stress. The effects of commonly used anesthesia drugs, opioids, and adjunct drugs on immune function are discussed. Patient populations at risk for increased morbidity due to perioperative immune depression are identified, along with patient-specific measures nurse anesthetists can take to reduce postoperative immune dysfunction.