From 1984 to 1989, 62 patients with palpable testicular tumor were examined with ultrasound before surgical exploration. The ultrasonographic morphology was compared with the histological diagnosis of the tumor. The radiologist's interpretation regarding the type of tumor (seminoma versus nonseminomatous tumor) was correct in 70%. The typical sonography of the seminoma comprises homogeneous, hypoechogenic and sharply delineated masses, but nonseminomatous tumors are inhomogeneous, hypoechogenic, normoechogenic and hyperechogenic masses with cysts and calcifications. The tumor stage could be predicted in precisely 44% of the seminomas and in only 8% of the nonseminomatous tumors. Nevertheless, the ultrasonogram of the testis may provide a false-positive tumor diagnosis. We conclude that ultrasonography may help us in the differential diagnosis of malignant tumors of the testis, but cannot replace surgical and histological exploration of the testis.