We introduced a technique of transurethral microwave coagulation of the prostate under transabdominal sector scanning. In 6 patients, this method was performed in order to relieve obstructive symptoms caused by prostatic cancer. In 10 patients with prostatic hypertrophy, this procedure followed by transurethral resection (TUR) was performed in order to eliminate hemorrhage during TUR. Transabdominal sector scanning gave us useful information during the microwave coagulation procedure. With this method, we were able to find the microwave applicator clearly which had a hyperechoic area and an acoustic shadow. Moreover, we could easily distinguish coagulated areas from noncoagulated areas because the ultrasonogram showed a hyperechoic region in the coagulated area. After the procedure, all patients with severe dysuria were able to void satisfactorily without any serious complications such as perforation or bleeding. Our clinical results indicate that transabdominal electronic sector scanning is a useful method during microwave coagulation of the prostate.