BACKGROUND: Women with endometriosis suffer from frequent symptoms despite multiple treatments in tertiary care. Although there is a need for a biopsychosocial perspective on endometriosis treatment, few conservative treatments have been investigated. We aimed to investigate the effects of a brief Mindfulness-Based Intervention (bMBI) in women with deep endometriosis who remain symptomatic despite undergoing conventional medical treatment. METHODS: A randomized controlled trial was performed with two groups: a standard medical treatment plus bMBI program and only standard medical treatment as a control. A total of 63 eligible participants were randomized to bMBI and control groups. The primary outcome was endometriosis-related pain, and secondary outcomes were quality of life and stress perception post-treatment. Analyses were carried out using multiple regression models. RESULTS: The results show that bMBI significantly improved pain unpleasantness (Cohen's f CONCLUSIONS: Our study suggests that bMBI is useful for managing endometriosis-related pain and restoring women's psychological well-being. SIGNIFICANCE: Brief Mindfulness-Based Intervention (bMBI) improved endometriosis-related pain and mental health compared to standard medical care. The present findings contribute to the applicability of MBI in visceral pain patients.