The present study was aimed to investigate short and long term memory abilities in person with Down syndrome (DS) and with intellectual Disability (ID) of different aetyology. For this purpose, we compared performances of 15 DS and 15 ID subjects with those of 30 normally developed subjects matched for mental age on tasks of verbal and visuo-perceptual explicit memory and on verbal repetition priming tasks. Our results document comparable verbal priming in the three groups. As for explicit memory, normal children performed better than MR individuals, and these, in turn, better than DS subjects. Compared to MR subjects, DS subjects were particularly deficient in organizing verbal material according to its categorial structure and in actively retrieving stored information. These results support the hypothesis that ID is not a uniform condition, characterised by an undifferentiated delay of the cognitive development, but rather that is charachetrised by a deficit in a complex cognitive system in which some cognitive abilities can be disrupted more than others.