Circular RNAs (circRNAs) are a species of RNAs with covalently closed loop structure and are widely expressed in eukaryocyte. Consisting of exons and/or introns, circRNAs are generated during the process of RNA splicing and are found to be relatively stable, evolutionally conserved and tissue/cell-specific. A few studies have indicated that circRNAs may participate in the RNA-RNA regulation network or RNA-protein complex formation and thus are involved in a diversity of diseases, including cancer. Here we reviewed the currently available outcomes and progress of researches concerning circRNAs and the potential relationship between diseases and circRNAs.