During the last 13 years, 2,080 infertile patients were subjected to diagnostic laparoscopy. The mean age was 32.3 and their mean infertility period was 6.0 years. Of these, 1,263(60.7%) patients were diagnosed to have endometriosis: 587(46.5%) were stage I (R-AFS), 348(27.6%) were stage II, 184(14.6%) were stage III and 144(11.4%) were stage IV. The age and the infertility period were almost the same among the stage of the disease. The overall pregnancy rate was 34.6%, after minimum 2 month follow up. The presence of endometriosis did not affect the prognosis of infertility: 34.2% pregnancy rate for patients with endometriosis, and 35.3% for those without endometriosis. There was an inverse relationship between the stage of the disease and the subsequent pregnancy rate: 37.8% for stage I, 34.8% for stage II, 32.1% for stage III and 20.8% for stage IV. But statistical significant difference was observed only between stage I and II, and stage IV. To elucidate the mechanism of endometriosis associated infertility, peritoneal fluid volume, intratubal sperm transport (peritoneal sperm recovery test), and phagocytosis of sperm in the tube and in the peritoneal fluid were examined in more than 1,000 cases. However, no positive relationship was found between the disease and these parameters. Fimbrial microbiopsy also revealed that endometriosis did not affect the ciliation index of the fimbria, nor changed the fine surface structure. Patients with minimal-mild disease were first managed expectantly for one year after laparoscopy: The pregnancy rate was 36.1% for stage I, and 29.7% for stage II. Ninety-eight patients who failed to conceive by expectant management were put on danazol therapy (600 mg/day, for 6 months). However, the results were very disappointing. Of 44 patients with stage I disease, only 3(6.8%) achieved a pregnancy, and none of 54 stage II patients conceived so far. Moreover, second-look laparoscopy revealed that danazol had no effect on the eradication of minimal-mild endometriosis. The patients with stage I-II disease were then treated exclusively by electrocautery at the time of initial laparoscopy: The pregnancy rate was 30.8% (57/185) for stage I, and 23.8% (25/105) for stage II. At second-look laparoscopy, 45.5% (10/22) of stage I and 73.7% (14/19) of stage II were disease free or improved, although the pregnancy rate was not so good as expected.(ABSTRACT TRUNCATED AT 400 WORDS)