This is a multi-center, randomized, double-blinded, placebo-controlled, parallel-group study (24-week treatment-comparison phase) with an open-label reference arm of active comparator (dienogest) followed by 28-week long-term treatment phase.

The primary objective of this study is to confirm the superiority of BAY86-5300 when administered with an extended flexible regimen for the treatment of endometriosis-associated pelvic pain in comparison to placebo in Japanese endometriosis patients within 24 weeks.

The secondary objective is to investigate the long-term safety of BAY86-5300 in patients treated with an extended flexible regimen for one year, and the bleeding pattern of BAY86-5300 when administered with an extended flexible regimen compared to dienogest.

Inclusion Criteria:

• Patients diagnosed as having endometriosis by laparotomy or laparoscopy, or by identification of chocolate cyst of endometriosis, or patients with the clinical diagnosis of endometriosis, who fulfill the condition of pelvic tenderness or induration of Cul-de-sac or uterine immobility
• Patient with pelvic pain judged by the highest Visual Analogue Scale (VAS) value of 40 mm or higher which is determined during 2 menstrual cycles before randomization (baseline observation phase)
• Patients having the normal menstrual cycle (25 to 38 days) in the latest two menses before randomization (baseline observation phase)
• Patients who do not wish to become pregnant during the course of the study

Exclusion Criteria:

• Patients who have organic diseases of which surgical treatment is prioritized by investigator
• Patients in whom any hormonal therapies, including combined oral contraceptives (COCs) and progestins, have failed for treatment of symptomatic endometriosis (moderate, severe pain)
• Patients for whom YAZ Combination Tablet is contraindicated (according to Japanese Labeling)
• Patients for whom dienogest is contraindicated (according to Japanese labeling of Dinagest Tab 1mg)