Spinal muscular atrophy (SMA) is a frequent autosomal recessive disease in human characterized by degeneration of motor neurons of the spinal cord. The genomic region containing the defective gene (5q13) is particularly unstable and prone to large-scale deletions whose characterization led to the identification of the survival motor neuron (SMN) gene, the SMA determining gene encoding a hitherto unknown protein. As an initial step toward the generation of a murine model for SMA, we identified and characterized a full-length murine Smn cDNA. The coding sequence of the mouse Smn gene was found to be 82% identical, at the amino acid level, with the human SMN coding sequence. The Smn locus was mapped to the segment of mouse chromosome 13 exhibiting conservation of synteny with human chromosome 5q11-q23, which contains the SMN gene. However, no evidence for a duplication of the Smn gene was found in the mouse, suggesting that the duplication reported in human is a recent evolutionary event.