BACKGROUND Many women who undergo diagnostic laparoscopy for chronic pelvic pain do not have pelvic pathology. This has led to an interest in psychological factors that might contribute to their experience of pain. This study was designed to evaluate the effects of diagnostic laparoscopy on women with chronic pelvic pain and to explore possible psychological mechanisms. METHODS Seventy-one women undergoing laparoscopy for chronic pelvic pain were randomly allocated to one of two groups waiting different lengths of time for laparoscopy. Women were interviewed before laparoscopy and were followed up 1 week, 3 months and 6 months afterwards. Pain was assessed with an interview measure, diaries and visual analogue scales. RESULTS Pain reductions were observed from before to after diagnostic laparoscopy. Regression analysis was used to identify factors which predicted improvements in pain. The hypothesis that psychological factors would predict improvements in pain was confirmed. Pain improvements after laparoscopy were predicted by beliefs about pain and the change in each woman's evaluation of the seriousness of her condition. Other than baseline pain, these psychological variables were the only ones to emerge as predictors of pain change despite exploratory analysis of over 40 other variables. CONCLUSIONS Diagnostic laparoscopy can have beneficial effects in women with chronic pelvic pain. These effects appear to be the result of psychological mechanisms. Further investigation of these mechanisms could help in the understanding and treatment of women with chronic pelvic pain.