The genus Schizosaccharomyces is presently comprised of three species, namely Schizosaccharomyces pombe, Schizosaccharomyces octosporus and Schizosaccharomyces japonicus. Here, we describe a hitherto unknown species, Schizosaccharomyces cryophilus, named for its preference for growth at lower temperatures than the other fission yeast species. Although morphologically similar to S. octosporus, analysis of several rapidly evolving sequences, including the D1/D2 divergent domain of the large subunit (LSU) rRNA gene, the RNA subunit of RNAse P and the internal transcribed spacer elements, revealed significant divergence from any previously characterized Schizosaccharomyces strain. Based on phylogenetic analysis of the D1/D2 domain of the LSU rRNA gene, S. octosporus is the closest known relative of S. cryophilus, with the sequences of the two species differing by 25 nucleotide substitutions (>4%). Sequencing of the S. cryophilus genome and phylogenetic analysis of all 1 : 1 protein orthologs confirmed this observation, and together with morphological and physiological characterization, supports the assignment of S. cryophilus as a new species within the genus Schizosaccharomyces. The type strain of the new species is NRRL Y-48691(T) (=NBRC 106824(T)=CBS 11777(T)).