Recent research suggests a significant relationship between verbal short-term memory and normal language development. Although poor short-term memory and impaired language are features of Down syndrome there has been little investigation of the relationship between these functions in this population, and no studies have included the nonword repetition test devised by Gathercole and Baddeley on which much of the evidence from normal development is based. This study reports the use of nonword repetition with 33 children and teenagers with Down syndrome aged from 5 to 18 years, and investigates the relationship between this test and other memory and language measures. Word repetition was included as an indirect control for the perceptual and speech impairments often associated with this group. Words were repeated significantly more successfully than nonwords and both these tasks were sensitive to word length. Nonword repetition was significantly correlated with age, and when age and nonverbal cognitive ability were controlled, nonword repetition was significantly correlated with all other language-based memory measures, i.e. auditory digit span, word span, sentence repetition, and fluency, and also with memory for a sequence of hand movements, but not with memory for faces or a visual digit span task. There was also a significant relationship between nonword repetition and receptive vocabulary, language comprehension, and reading. When performance on the word repetition task was controlled in addition to age and nonverbal ability, significant correlations between nonword repetition and word span, sentence memory, hand movements, language comprehension, and reading remained. Fewer relationships between auditory digit span and these other measures were established; in particular, there was no association between digit span and the language and reading measures. Results suggest that nonword repetition is a reliable measure of phonological memory in Down syndrome and can predict language comprehension and reading ability.