Over 50% of patients still experience pain a year after mastectomy with or without lymphadenectomy. We aimed to determine the association between anesthetic technique, acute postoperative pain intensity, and the development of chronic postoperative pain. Forty patients were randomly assigned to receive general anesthesia with or without a paravertebral nerve block for modified radical mastectomy. Postoperative pain was assessed on a visual analog scale at 60 minutes and 24 hours; the patients were also asked to respond to a telephone questionnaire on chronic pain 4 to 5 months later. No significant differences in acute pain were observed. Twenty-nine responded to the telephone questionnaire. Only 1 patient in the paravertebral block group reported chronic neuropathic pain and none had phantom breast pain. Only 1 patient (6.7%) in the paravertebral block group reported chronic neuropathic pain and none had phantom breast pain. In the group that received general anesthesia alone, 1 patient reported phantom breast pain and 6 patients had neuropathic pain, associated with phantom breast pain in 2 cases (incidence of chronic pain 50%; P = .01, Fischer exact test; relative risk, 7.5, 95% confidence interval, 1.0-53.5). The incidences of myofascial pain (neck muscle tightness) were similar in the 2 groups. Four to 5 months after mastectomy, fewer cases of chronic pain developed in the group operated under general anesthesia with a preincisional paravertebral block than in the group that received only general anesthesia, with postoperative morphine chloride for analgesia.