The purpose of the study is to evaluate the efficacy and safety of two doses of ERB-041 (75 mg and 150 mg) relative to placebo on the relief of endometriosis-related symptoms (dysmenorrhea, pelvic pain, and deep dyspareunia) in reproductive aged women.

Inclusion Criteria:

• Surgical diagnosis of endometriosis within the last 10 years
• Sexually active, nonpregnant, nonlactating women (18-45 years) with regular menstrual cycles who are willing to use non-hormonal contraception

Exclusion Criteria:

• Conditions requiring the use of chronic pain therapy
• Prophylactic use of analgesics to avoid endometriosis-related pain