Müllerianosis is a rare benign lesion of the urinary bladder, which is constituted by two or more of the Müllerian-duct-derived tissues. We report a 45-year-old perimenopausal multiparous woman presenting with occasional episodes of dysuria and lower abdominal discomfort of recent duration. Ultrasound examination revealed a well-defined lesion in urinary bladder and the absence of left kidney. Contrast-enhanced CT of the abdomen confirmed the findings. During diagnostic cystoscopy, haemorrhagic polypoidal lesions were noted in the left side of the posterolateral wall and dome of urinary bladder along with the absence of left ureteric orifice. Transurethral resection of the bladder lesions was done and histology examination confirmed the diagnosis of Müllerianosis. She was administered Luteinizing hormone-releasing hormone (LHRH) agonist monthly. At 1 year of follow-up, cystoscopy showed only scar tissue. The case was reported for the rarity of Müllerianosis noted in a patient with unilateral agenesis of kidney, a possible cause of delayed presentation.