Renal cysts in childhood can be found in a variety of diseases, which can be congenital or acquired, or renal cysts may be part of a multiorgan disease or restricted to the kidneys only. Ultrasonography is the first-line diagnostic tool and is informative in many cases. However, there is a broad spectrum in the sonographic appearance of renal cysts, and family or genetic studies, a search for extrarenal organ involvement, or additional imaging modalities may be required to make a definitive diagnosis. The aim of this article is to summarize the diagnostic potential and limitations of ultrasonography and depict typical examples of the most important cystic entities.