Renal cysts are common findings in urologic and nephrologic ultrasound imaging. In addition to a thorough anamnesis, it is important to differentiate between harmless “blank” kidney cysts, which can be found in around 30% of the population during ultrasound examinations over the course of their life; these appear strictly anechoic on B-scan ultrasound. Round, non-echoic formations on ultrasound examination are often called “complicated” kidney cysts in clinical practice and require further clarification using additional ultrasound modalities. Contrast-enhanced sonography has established itself as a problem solver in many clinical centers. Unclear “complicated cysts” are then classified using the CEUS-Bosniak classification and ideally discussed in an interdisciplinary tumor board. The CEUS-Bosniak-III and CEUS-Bosniak-IV lesions require a supplementary CE-CT or CE-MRI examination, which should then be discussed together with the ultrasound videos in an interdisciplinary tumor conference.