Eighteen patients with the post-mastectomy pain syndrome (PMPS) form the basis of this study. PMPS probably occurs in a minority of women after mastectomy. The onset of persistent pain usually occurred immediately or very shortly after the operation. The pain location or sensory findings implied involvement of the territories of other cutaneous branches of the intercostal nerves as well as the intercostobrachial nerve. A variety of treatment approaches were unsatisfactory. Twelve of 14 patients completing treatment with topical 0.025% capsaicin showed improvement after 4 weeks and 8 (57%) were judged to be good or excellent responses. Six months after the trial's completion 50% of those followed continued to have good pain relief. This therapy should now be subjected to a randomized, double-blind, placebo-controlled trial.