Sulphamidase is an exoglycosidase involved in the degradation of heparan sulfate. Lack of sulphamidase activity leads to the lysosomal storage disorder Mucopolysaccharidosis type IIIA (Sanfilippo type A OMIM No. 252900). At present there are no naturally occurring small animal models of this disease that could be of fundamental importance to study the pathophysiology of the disease and to try therapeutic strategies. Cloning of the mouse gene is an important step to create a mouse model for this common mucopolysaccharidosis. We have isolated and sequenced the gene encoding mouse sulphamidase. Comparison of the deduced amino acid sequences of human and mouse sulphamidase showed 88% identity and 93% similarity. The exon-intron structure of the gene has been determined with the mouse 10-kb gene divided in 8 exons. The mouse sulphamidase gene (Sgsh) was mapped to the distal end of Chromosome (Chr) 11, in a region that is homologous with a segment of human Chr 17 containing the orthologous human gene.