This study explored the hearing capabilities of Down Syndrome (DS) adolescents and young adults relative to a matched sample of non-DS trainable mentally handicapped (MH) individuals, and examined the relationship between hearing ability and performance on several cognitive tasks. Samples of 26 DS and 26 MH individuals were matched on intelligence quotient (IQ) and chronological age (CA). Audiometric data revealed greater DS than MH hearing losses at five of the six tested frequencies, more DS conductive and mixed hearing losses, and particularly high DS losses in the high frequency range. Measurement of the speech reception threshold revealed poorer reception of speech by the DS than the MH group. Classification of tympanograms indicated fewer normal ears and twice as many DS ears with middle ear problems reflecting no mobility or retraction of the tympanic membrane. Presence of DS middle ear difficulties was also confirmed by poorer elicitation of the acoustic (stapedius) reflex in DS subjects. Correlation of hearing variables with seven cognitive tasks revealed only one significant relationship after statistical removal of the effects of CA and IQ: DS subjects with poorer hearing identified fewer words in a task in which a masking noise quickly followed a spoken word. (45 reference) (JDD)