Endometriosis is the presence of tissue that resembles endometrium outside the uterus. This tissue responds to hormonal stimulation just as the uterine lining does. The lesions may cause pain, pressure, and inflammation to adjacent organs as they build up and slough during menstrual cycles.
Endometriosis causes pain in many women that is either sharp or dull. It is more constant than the spasmodic pain of dysmennorea (painful periods). Dyspareunia (painful sexual intercourse) may be present. Endometriosis appears to cause infertility in some women.