Usher's syndrome, type 3 (USH3) is characterized by progressive hearing loss. Usher's syndrome, type 3 has been supposed to be rare, occurring in 2% to 4% of all patients with Usher's syndrome. In a nationwide study we collected data on 229 patients with Usher's syndrome in Finland. Definite cases of USH3 were found in 30 (13%) of the 229 patients. An additional 61 patients had clinical evidence of earlier progression of their hearing impairment. We suggest that 91 (40%) of the 229 patients with Usher's syndrome represent cases of USH3.