• The hearing status of 18 patients with Morquio's syndrome (mucopolysaccharidosis IV) was evaluated. All three patients under age 8 years had a conductive hearing loss. Fourteen of 15 patients 8 years of age and older had a mixed or sensorineural hearing loss; one had normal hearing. Six patients wore hearing aids. By the end of the first decade of life, most persons with Morquio's syndrome may be expected to have either a mixed or sensorineural hearing loss. Amplification may be required.