The gene coding for cystatin D (CST5), a cysteine proteinase inhibitor, was mapped by fluorescent in situ hybridization to human chromosome 20p11.21. This assignment, together with previous data on mapping of members of the cystatin gene family, indicates that cystatin family II genes are all clustered on the short arm of chromosome 20, whereas cystatin family I and III genes are located on the long arm of chromosome 3.