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Background and purpose: Endometriosis is a chronic and debilitating disease which is associated with a variety of morbid symptoms. This study aimed at exploring the perception and experiences of patients with endometriosis about pain. Materials and methods: A qualitative research was performed in 18 patients with endometriosis attending Arash Hospital (Tehran, 2014). They were selected by purposive sampling. Data was collected by semi-structured interview and analyzed using a conventional content analysis. Results: Two main themes emerged from the participants' experiences: 1) disruption of individual and family life and 2) feelings of threat and vulnerability. The first theme included two categories: suffering varied and diffused pain and disruption of sexual activity. Categories of the second theme were: complaints of severe and intolerable pain and various actions taken to reduce the pain. Conclusion: The findings suggest that patients with endometriosis suffer various pains that influence different parts of the body. These pains are often felt with great intensity and may have devastating consequences on their lives. Deep attention should be paied to the symptoms of these patients and health authorities should not trivialize their pain so that early diagnosis is made and suitable interventions are performed to promote such patients’ health.