Background: MicroRNAs (miRNAs) are short non-coding RNAs that regulate gene expression via binding to the 3′ ends of mRNAs. MiRNAs have been associated with many cellular events ascertaining their central role in gene regulation. In order to better understand miRNAs of interest it is of utmost importance to learn about the genomic conservation of these genes. Findings. The miRviewer web-server, presented here, encompasses all known miRNAs of currently fully annotated animal genomes in a visual 'birds-eye' view representation. miRviewer provides a graphical outlook of the current miRNA world together with sequence alignments and secondary structures of each miRNA. As a test case we experimentally examined the expression of several miRNAs in various animals. Conclusions: miRviewer completes the homologous miRNA space with hundreds of unreported miRNAs and is available at:.