To examine the effect on pain and quality of life for women with all stages of endometriosis undergoing laparoscopic surgery compared with placebo surgery. A randomized, blinded, crossover study. A tertiary referral unit in a district general hospital. Thirty nine women with histologically proven endometriosis completed the 12- month study. Women were randomized to receive initially either a diagnostic procedure (the delayed surgical group) or full excisional surgery (the immediate surgery group). After 6 months, repeat laparoscopy was performed, with removal of any pathology present. The end points were changes from baseline values of visual analogue pain scores, validated quality of life instruments (EQ- 5D and SF- 12), and sexual activity questionnaire scores. Patients and assessors of outcomes were blinded to the treatment group assignment. Significantly more of the 39 women operated on according to protocol reported symptomatic improvement after excisional surgery than after placebo: 16 of 20 (80% ) vs. 6 of 19 (32% ); χ 2(1) = 9.3.Other aspects of quality of life were also significantly improved 6 months after excisional surgery but not after placebo. Progression of disease at second surgery was demonstrated for women having only an initial diagnostic procedure in 45% of cases, with disease remaining static in 33% and improving in 22% of cases. Nonresponsiveness to surgery was reported in 20% of cases. Laparoscopic excision of endometriosis is more effective than placebo at reducing pain and improving quality of life. Surgery is associated with a 30% placebo response rate that is not dependent on severity of disease. Approximately 20% of women do not report an improvement after surgery for endometriosis. To examine the effect on pain and quality of life for women with all stages of endometriosis undergoing laparoscopic surgery compared with placebo surgery. A randomized, blinded, crossover study. A tertiary referral unit in a district general hospital. Thirty nine women with histologically proven endometriosis completed the 12- month study. Women were randomized to receive initially either a diagnostic procedure (the delayed surgical group) or full excisional surgery (the immediate surgery group). After 6 months, repeat laparoscopy was performed, with removal of any pathology present. The end points were changes from baseline values ​​of visual analogue pain scores, validated quality of life instruments (EQ-5D and SF-12), and sexual activity questionnaire scores. Patients and assessors of outcomes were blinded to the treatment group assignment. Significantly more of the 39 women operated on according to protocol reported symptomatic improvement after excisional surgery than aft er placebo: 16 of 20 (80%) vs. 6 of 19 (32%); χ 2 (1) = 9.3. Of aspects of quality of life were also significantly improved 6 months after excisional surgery but not after placebo. Progression of disease at second surgery was demonstrated for women having only an initial diagnostic procedure in 45% of cases, with disease remaining static in 33% and improving in 22% of cases. Nonresponsiveness to surgery was reported in 20% of cases. Laparoscopic excision of endometriosis is more effective than placebo at reducing pain and improving quality of life. Approximately 20% of women do not report an improvement after surgery for endometriosis.