Background <p>Endometriosis is a common estrogen-dependent disorder that typically affects women of reproductive age and generally resolves following menopause. This report describes a rare case of postmenopausal bladder endometriosis (BE) occurring in a woman with a normal body mass index and no history of exogenous estrogen use.</p> Case presentation <p>A postmenopausal woman with a normal body mass index and no history of estrogen replacement therapy presented with dysuria. Clinical examination and imaging suggested bladder endometriosis. The patient underwent laparoscopic partial cystectomy with total hysterectomy and bilateral salpingo-oophorectomy. Postoperative histopathology confirmed the diagnosis of endometriosis.</p> Conclusions <p>This case demonstrates that BE can occur in postmenopausal women in the absence of exogenous estrogen or obesity. The coexistence of liver cirrhosis, associated with impaired estrogen metabolism, and diabetes, characterized by chronic inflammation, may synergistically contribute to a pro-inflammatory microenvironment that sustains local estrogen activity, enabling lesion persistence. Clinicians should consider such systemic factors in non-obese postmenopausal women presenting with symptoms suggestive of endometriosis.</p>