High-dose cyclophosphamide (CY) is associated with a high risk of hemorrhagic cystitis. The reported frequency ranges from 6.5 to 52% despite the use of hydration protocols. The current study reports a hyperhydration and continuous bladder irrigation protocol which resulted in a very low incidence of microscopic hematuria and no reported cases of visible hematuria. Patients received baseline fluids at 200 ml/m2/h during chemotherapy. Additional fluid boluses were given if urine output fell below 200 ml/h. Bladder irrigation was performed at a rate of 1 l/h during and for 24 h after high-dose CY. Three hundred three evaluable patients with solid tumors received high-dose chemotherapy with CY at a dose of 5625 mg/m2 over 3 days. Patients also received cisplatin 165 mg/m2 and carmustine 600 mg/m2. Some patients received thiotepa 300-750 mg/m2 instead of carmustine. The overall incidence of microscopic hematuria (> 15 RBCs per high power field) was 19%, with only 11% of patients experiencing more than 50 RBCs per high power field. No patient developed visible hematuria or symptomatic hematuria requiring intervention. These results using aggressive hyperhydration and high volumes of continuous bladder irrigation are among the best reported following high-dose CY chemotherapy.