Massive hematuria, which is most frequently caused by radiation for pelvic malignancies, after treatment with cyclophosphamide or secondary to aggressive anticoagulation, represents a vexing problem for the practicing urologist. The existence of numerous therapeutic approaches results from the lack of an effective therapeutic modality. Lately, formalin seems to offer a new hope for the treatment of intractable hematuria. Analysis of published results after treatment with formalin revealed generally excellent results regarding control of hematuria. Nevertheless, the complication rate of formalin application is surprisingly high, including vesicoureteral reflux and hydroureteronephrosis as local reactions and systemically tubular necrosis with anuria. Our series of patients is presented with a detailed description of a patient who was afflicted with a vesicovaginal fistula following formalin instillation. Formalin can serve as excellent therapy for massive hematuria. If attention is paid to the concentration and to the technical details of its instillation the noxious side effects can be minimized or prevented in the majority of cases.