Renal cell carcinoma (RCC) is the most common malignant tumor of the kidney. The major goal of imaging techniques is to correctly differentiate between benign and malignant renal lesions. We present the cases of six patients with renal masses that were interpreted completely differently based on ultrasound (US) and computerized tomography (CT) findings.From January 1st, 2008 to March 1st, 2014, 307 patients from our center underwent nephrectomy for RCC. In all patients US and CT were performed before the operation.In six patients, the US indicated a focal, solid renal lesion that was interpreted by CT as a cystic lesion (Bosniak II-III). Because discrepancies were evident, renal biopsies were performed. The biopsies revealed RCC in the six patients, all of whom underwent subsequent nephrectomy. All of the patients were confirmed to have macroscopically solid RCC without any cystic components.In most cases, CT is the most accurate diagnostic technique for the clinical diagnostic classification of renal masses. In cases where US characterizes a renal lesion as solid, despite CT findings of a cystic lesion, kidney biopsies are recommended. The 6 cases reported here support our belief that, in diagnostic processes of RCC, these techniques should be complementary used.