Patients scheduled for operation on suspected endometriosis in two study hospitals specialized in the surgical treatment of endometriosis between January 2005 - December 2007 (Päijät-Häme Central Hospital) and January 2008 - December 2008 (Helsinki University Hospital) were enrolled to the study. The diagnosis of endometriosis was histologically verified for all patients. Background data was collected from patients` age, body mass index, previous deliveries, previous endometriosis surgery, and current hormonal treatment for endometriosis.