Introduction. Bladder mullerianosis is a rare and proliferative lesion that contains at least two types of ectopic Mullerian tissue in its wall. Aim. To present case of bladder mullerianosis. Description of case. The text contains a description of a clinical case of a 50-year-old woman admitted to a gynecological ward due to diarrheal symptoms and abdominal pain. In a CT examination of the abdominal cavity with contrast, within the posterior left-sided wall of the bladder a 43x25mm proliferative lesion suggestive of neoplastic character was revealed. Transurethral resection of the lesion (TURB) was performed. Histopathology revealed endosalpingiosis with small endocervical foci. The picture of hyperplasia met the criterion of mullerianosis. Conclusion. Bladder Mullerianosis is a very rare disease that occurs mainly in women of reproductive age. It has very good prognosis. It is important to differentiate the lesion with malignant tumor. The basis for the diagnosis is the histopathological examination of the lesion tissues taken during the surgery.