To estimate the laparoscopic frequency of endosalpingiosis versus other causes of peritoneal proliferation.Clinic-based, prospective, nonrandomized study (Canadian Task Force classification II-2).University-affiliated hospital.The 1107 consecutive women undergoing laparoscopy over 1 year.Peritoneoscopy was performed during laparoscopy. All peritoneal proliferations were excised and examined by histology.In 7.6% of patients there was histologic evidence of endosalpingiosis. The frequency in asymptomatic women undergoing elective sterilization was 8.3%, and in infertile patients it was not significantly higher (11.7%, p = 0.6765). No significant difference was seen between patients with (7.3%) and without (7.9%) lower abdominal pain (p = 0. 7027).Endosalpingiosis is the second most common cause of peritoneal proliferation in the lower abdomen, with histologic evidence of the disorder in more than 7% of premenopausal women. In contrast to endometriosis, endosalpingiosis plays only a minor role in the evaluation of infertility and lower abdominal pain. Because of its relationship to serous ovarian neoplasms of low malignant potential, further prospective studies are urgently needed.