OBJECTIVE: To determine whether the use of patient-controlled analgesia vs intramuscular injections improves postoperative psychological parameters, particularly anxiety. DESIGN: Randomized, controlled trial of patient-controlled analgesia vs as-needed intramuscular morphine with pre- and postoperative assessments of pain, mental status, narcotic use, anxiety and mood states. SETTING: General surgical wards and surgical intensive care unit at a Veterans Administration hospital. PATIENTS: Eighty-three elderly, chronically ill males undergoing major elective surgery. INTERVENTION: Subjects randomized to receive postoperative patient-controlled analgesia vs as-needed intramuscular morphine. Pre- and postoperative assessments of State-Trait Anxiety Inventory, McGill-Dartmouth Part IV and Short Portable Mental Status Questionnaire. Pain (using linear analog scale), sedation score and narcotic use assessed every 4 hours for 72 hours. RESULTS: No differences were found in state anxiety or self-perceived mood states. Postoperative state anxiety was found to relate most closely to preoperative anxiety and postoperative complications, rather than method of analgesia or severity of pain. However, patient-controlled analgesia subjects had significantly improved analgesia and increased satisfaction. CONCLUSION: The use of patient-controlled analgesia does not significantly alter the measured psychological parameters, compared with intramuscular injections. Improved analgesia is the result of pharmacologic effects, independent of psychological factors.