Circular RNAs (circRNAs) represent a recent research hotspot in the RNA field. Reports are linking heterogeneous circRNA groups and many different human disorders, especially cancer. In this review, we focused on the rapidly advancing field of circRNAs that are involved in human diseases. First, we discuss tools (for example, public databases) that scan genome spans of interest to identify known circRNAs. Second, we present disease-oriented circRNAs and discuss their relationship with the disease. Finally, we envision current and potential circRNA research applications in treating human diseases. CircRNAs provide new insights into the “dark matter” of the human genome and may serve as diagnostic or predictive biomarkers of disease and new potential therapeutic targets. (By Dr. Xubao Liu, http://jmg.bmj.com/content/early/2016/03/03/jmedgenet-2016-103758 )