Eosinophilic cystitis is an unusual bladder lesion of unclear etiology first described in 1960. It usually causes irritative voiding symptoms and hematuria and in its rare tumor-like appearance the disease may mimic an invasive bladder neoplasm. In the report herein, a case of an 11-year-old boy with a tumor-forming eosinophilic cystitis is presented which was mistaken for an infiltrative vesical malignancy until the histopathological study was completed. The principal clinical findings, differential diagnosis, etiology, pathogenesis and treatment modalities of this inflammatory disease are discussed.