The purpose of this investigation was to determine how well Down Syndrome (DS) adolescents and young adults, relative to other mentally handicapped (MH) individuals, comprehend single words and simple sentences. Samples of 26 DS and 26 MH individuals were matched on intelligence and chronological age and were administered audiological, language, and memory tests. Results suggested that although DS and MH peers show similar understanding of single words and simple grammatical constructions, DS individuals are less able to understand grammatically difficult sentences--a limitation that may reflect, in part, a general difficulty with precisely remembering sequences of spoken words. Multiple partial correlations (with the effects of intelligence and chronological age statistically removed) further indicated that for each group: (1) sentence and word comprehension were unrelated; (2) sentence comprehension was positively related to expressive language ability and auditory short-term memory; and (3) neither sentence nor word comprehension correlated with hearing sensitivity. (31 references) (JDD)