In this study, we compared the effects of two analgesic regimens on perioperative nitric oxide index (NOx) and the likelihood of subsequent development of chronic postsurgical pain (CPSP) after breast surgery and sought to determine the association among early postoperative pain, NOx, and the likelihood of subsequent development of CPSP. Twenty-nine consecutive ASA I or II patients undergoing breast surgery with axillary clearance were randomly allocated to one of two groups. Patients in group S (n = 15) received a standard intraoperative and postoperative analgesic regimen (morphine sulfate, diclofenac, dextropropoxyphene hydrochloride + acetaminophen prn). Patients in group N (n = 14) received a continuous paravertebral block (for 48 h) and acetaminophen and parecoxib (followed by celecoxib up to 5 days). Visual analog scale pain scores at rest and on arm movement were recorded regularly until the fifth postoperative day. A telephone interview was conducted 10 wk postoperatively. The McGill Pain Questionnaire was used to characterize pain. NOx was estimated preoperatively, at the end of surgery, 30 min and 2, 4, 12, 24, 48 h postoperatively. Twelve (80%) patients in group S and no patient in group N developed CPSP (P = 0.009). Compared with patients with a pain rating index > or =1 (n = 18) 10 wk postoperatively, patients with a pain rating index = 0 (n = 11) had lesser visual analog scale pain scores on movement at each postoperative time point from 30 min until 96 h postoperatively (P < 0.005) and at rest 30 min (0.6 +/- 1.5 versus 30.2 +/- 26.8; P = 0.004), 4 h (2.3 +/- 7.5 versus 19.0 +/- 25.8; P = 0.013), 8 h (4.4 +/- 10.2 versus 21.4 +/- 27.0; P = 0.03) and 12 h (0.7 +/- 1.2 versus 15.4 +/- 27.0; P = 0.035) postoperatively. NOx values were greater in group N compared with group S 48 h postoperatively (40.6 +/- 20.1 versus 26.4 +/- 13.5; P = 0.04).