Circular RNAs (circRNAs), a new class of regulatory noncoding RNAs, play important roles in human diseases. While a growing number of circRNAs have been characterized with biological functions, it is necessary to integrate all the information to facilitate studies on circRNA functions and regulatory networks in human diseases. Circ2Disease database contains 273 manually curated associations between 237 circRNAs and 54 human diseases with strong experimental evidence from 120 studies. Each association includes circRNA name, disease name, expression pattern, experimental method, a brief functional description of the circRNA-disease relationship, and other detailed information. The experimentally validated miRNAs that may be 'sponged up' by these circRNAs and their validated targets were also integrated to form a comprehensive regulatory network. Circ2Disease provides a user-friendly interface to browse, search, analyze regulatory network and download data. With the rapidly increasing interest in circRNAs, Circ2Disease will significantly improve our understanding of circRNA deregulation in diseases and is a useful resource for studying posttranscriptional regulatory roles of circRNAs in human diseases.