Typical dental changes were present in all cases, although they were of variable degree. However, the tooth morphology would appear to be highly specific for MPS IV A, and is not found in MPS IV B (beta-galactosidase deficiency) or the recently delineated MPS IV C (enzyme defect unknown). Thus the dental changes have a very useful diagnostic potential in mild atypical cases of MPS IV A, although they may only be demonstrable radiologically in some such cases.