Twenty-four children with dyslexia (aged 7;7 to 12;1) and twenty-four age-matched controls named pictures aloud while hearing nonsense syllables either phonologically related (i.e., part of) or unrelated to the target picture name. Compared with controls, dyslexics had slower reaction times overall and, for low frequency items, the degree of facilitation from phonologically related sound segments relative to unrelated segments was proportionally greater. Within the dyslexic group, phonological facilitation was greater and picture naming speed slower for poorer compared with better readers. Phonological facilitation and picture naming speed was unrelated to reading ability in the normal readers. The results suggest that phonological encoding during speech production is less efficient in some children with dyslexia and that hearing part of the target word strongly facilitates this process. The findings are consistent with the hypothesis that dyslexia can arise from poorly specified output phonological representations. (Contains 2 footnotes, 2 tables and 3 figures.)