A Japanese boy with ataxia telangiectasia (AT) developed severe gross hematuria and recurrent bladder tamponade, requiring an extensive blood transfusion. He had received intermittent intravenous cyclophosphamide pulse therapy (cumulative dose of 1.3 g) for refractory steroid-resistant and intravenous immunoglobulin-resistant severe autoimmune thrombocytopenia 3 years previously. A cystoscopy revealed multiple varices and severe telangiectasias in the bladder wall. The intensive treatment, such as repeatedly selective embolization of the vesical arteries, proved to be partially effective. Finally, a surgical cystotomy resulted in a gradual improvement in clinical symptoms. To the best of our knowledge, this is the first report of a patient with AT who developed refractory bladder hemorrhage caused by widespread vesical telangiectasias.