Usher syndrome type III is an autosomal recessive disorder characterized by progressive sensorineural hearing loss, vestibular dysfunction, and retinitis pigmentosa. The disease gene was localized to 3q25 and recently was identified by positional cloning. In the present study, we have revised the structure of the USH3 gene, including a new translation start site, 5′ untranslated region, and a transcript encoding a 232–amino acid protein. The mature form of the protein is predicted to contain three transmembrane domains and 204 residues. We have found four new disease-causing mutations, including one that appears to be relatively common in the Ashkenazi Jewish population. We have also identified mouse (chromosome 3) and rat (chromosome 2) orthologues, as well as two human paralogues on chromosomes 4 and 10.