OBJECTIVE The indications of partial nephrectomy have expanded after the introduction of new techniques for preventing excessive blood loss and avoiding deterioration of the renal function after clamping the renal pedicle. We present our clinical experience of partial nephrectomy for renal tumors using a microwave tissue coagulator. METHODS Between April 1996 and January 2000, 34 patients underwent open partial nephrectomies in the Kobe City General Hospital. The microwave tissue coagulator was used for resection of the renal parenchyma, but in deeper lesions a sharp dissection was performed. Twenty-two patients (groups 1 and 2) underwent partial nephrectomy without vascular control (14 renal pedicles were not disturbed in group 1 patients, and 8 renal pedicles were dissected but not clamped in group 2 patients). Another 12 patients (group 3) underwent vascular control with ligation of the tumor-feeding segmental arteries before parenchymal resection. The patients of group 1 underwent wedge resections, while those of groups 2 and 3 underwent segmental or transverse partial nephrectomies. RESULTS Complete tumor resection was done in all 34 patients. In group 1, the microwave tissue coagulator was very effective to control the blood loss (mean 330 ml). In larger resections, this method only was inadequate to control the blood loss (mean 489 ml in group 2), so that we needed vascular control. However, despite vascular control, mean blood losses of about 943 ml because of deeper venous bleeding occurred in group 3, and, moreover, postoperative renal infarctions occurred in 2 patients. Other complications were urinary fistula formation in 16 patients (47%) and renal pelvic stenoses in 2 patients (5.8%). All of the urinary fistulas were easily repaired by simple suturing intraoperatively. CONCLUSIONS Especially in wedge resection, the microwave tissue coagulator achieved safe resection without vascular control which differs from other new techniques. However, in larger resections, a combination with other techniques may be necessary to decrease blood loss and the rate of complications.