We recently treated a 51-year-old man who presented a bladder mass that mimicked neoplasm. The patient had urinary frequency, suprapubic pain, and gross painless hematuria. The bladder mass was detected incidentally by abdominal sonography. MRI revealed a wide-based bladder tumor in the right posterior bladder wall with muscle infi ltration. Transurethral
resection of the bladder tumor (TURBT) showed eosinophilic cystitis (EC), and the patient was treated with a combination of corticosteroids, antibiotics, and antihistamines. He experienced a marked improvement during the 6-month follow-up period. EC is a rare disease with an unknown etiology that mimics many other urological conditions. In addition to clinical symptoms of urinary frequency, dysuria, hematuria, and suprapubic pain, the disease may present with a bladder mass mimicking invasive bladder cancer. Resection of the lesion is mandatory, and consideration should be given to systemic treatment, including corticosteroids, antihistamines, and antibiotics. Early detection and prompt treatment usually result in good outcomes.