BGS649 Monotherapy in Moderate to Severe Endometriosis Patients

Inclusion Criteria: * Premenopausal women with documented moderate to severe endometriosis. Occurrence of three sequential menstrual cycles of 24-35 days duration prior to enrollment. * Laparoscopically proven diagnosis of moderate to severe endometriosis (diagnosed within the past 10 years before screening). * Patients not planning to become pregnant within one year after the screening visit and willing to use two effective methods of non-hormonal, barrier birth control for the duration of the study or who are surgically sterile. * Patients must have a score of at least 4 on the numerical rating scale (NRS) for one of the following three pain measurements: pelvic pain, menstrual pain and dyspareunia Exclusion Criteria: * Estrogen replacement therapy using either prescription medications or estrogen-containing OTC nutritional/herbal supplements such as soy extracts or topical estrogens. * Aromatase inhibitor therapy (includes Femara (letrozole), Aromasin (exemestane) or Arimidex (anastrozole) within the past 12 months. * Oral bisphosphonate therapy (i.e. Fosamax (alendronate)) within the past 6 months or intravenous bisphosphonate (i.e., Reclast, pamidronate) \< 15 months from screening. * Systemic glucocorticoid therapy within the past 4 weeks. * Contra-indications to oral contraceptive use. Other protocol-defined inclusion/exclusion criteria may apply