Several cross-sectional studies and one longitudinal study were conducted on the language abilities of various cohorts of persons with Down syndrome aged between 14 and 50 years. No significant difference was observed on any of the receptive and productive morphosyntactic and lexical measures used, suggesting no marked change in the language of these persons from adolescence onto late adulthood. Repeated measures of cerebral metabolic rate (CMR) for fluorodeoxyglucose using a Positron Emission Tomography were made over a 4-year interval with 7 participants with Down syndrome aged between 37 and 49 years. A gradual decrease in global CMR for both cerebral hemispheres and for each participant was documented. It was particularly marked for 3 participants. However, no language deterioration could be associated with their marked lowering in CMR.