We report two cases of small renal adenocarcinoma and one case of small angiomyolipoma, which were identified as hyperechoic tumors by ultrasonography. None of the three tumors displayed fat content on plain CT. Since CT cannot reliably identify the intratumoral structure of small hyperechoic renal tumors, we recommend intraoperative pathological examination when CT findings do not correspond with the results of ultrasonography.