Ultrasound was used to detect the location of, and to measure the size of undescended testis. The patient was laid in a supine position, and the ultrasonic probe was manipulated over the inguinal region. We employed the immersed technique, by which the probe was used in a water bag over the target region, and employed another technique, by which testis was scanned sandwiching by Kitecko sonojelly® between ultrasonicprobe and skin. Ultrasonographic findings of undescended testis was as follows: the shape of undescended testis is expressed as round or oval, the internal echoes are almost homogenous and the border is almost clear. The ultrasonographic evaluation of the location and the size of undescended testis was correlated well with the actual condition found on operation. Among 8 cases of nonpalpable undescended testes, 6 testes were visualized on ultrasonogram but 2 testes were not. Preoperative laparoscopy was performed on 2 cases with the ultrasonographically unrevealed testis. One was detected spermatic vein and vas deferens by laparoscopy and was found atrophic testis at the external inguinal ring on operation. And the other was not detected spermatic vein and vas deferens by laparoscopy, and was diagnosed monorchidism. Preoperative laparoscopy is thus very useful in cases in which ultrasonography fail to detect undescended testis.