Database of fungal genome size information has been launched in 2005: the Fungal Genome Size Database (http://www.zbi.ee/fungal-genomesize/). The database provides freely accessible genome size data assembled from literature. The taxonomy and the names of the used updated species follow Index Fungorum (http://www.indexfungorum.org). Genome size data are given as haploid (1C) values in megabases (Mb) and in picograms (pg). The database offers flexible search facility. The data can be queried by different taxonomical levels (phylum, order, genus, species epithet, variety) as well as by ploidy level, chromosome number, chromosome size range, method of genome size estimation, standard specimens used, cell type analyzed, and source reference. Responses to queries are presented as tables, with detailed information about given records (e.g., herbarium index, original reference, and additional remarks) provided in a separate pop-up window accessed by clicking on a given genus or species name in the main table. Such data are of significant importance to the genomics community both as fundamental features of genome structure and as direct estimators of the cost of complete sequencing programs.