Testicular microlithiasis was sonographically diagnosed in 16 patients. Using high-frequency transducers, the typical speckled pattern with multiple small bright echoes generated by intratubular calcifications appeared in the sonograms. The finding was bilateral in all but one patient who had previously undergone semicastration for testicular cancer and subsequent irradiation. In 6 cases a testicular tumor was present and visible in the sonogram. Sonography was performed in another 6 cases because of varicocele or epididymal cysts. The spermiograms and tumor marker levels of these patients were within the normal range, and there was no evidence of an extragonadal germinal tumor. Three patients presented with oligozoospermia, 1 thereof with hypogonadism. In 7 cases the sonographic diagnosis was histologically confirmed, i.e. multiple calcifications were found within the seminiferous tubules. The etiology and clinical significance of this rare phenomenon are unclear. Testicular microlithiasis is asymptomatic and also found in otherwise normal testes. However, in contrast to normal testes, a high percentage of testicular tumors is known to be associated with microcalcifications. In the presence of a definite sonographic diagnosis, exclusion of malignancy and sonographic follow-up are therefore indicated, as in the present series 44% of cases presented with testicular tumors.