The speech of children with Down's syndrome (DS) is often unintelligible, unlike many other children who have an intellectual disability. However, the nature of their speech disorder is controversial. The speech error patterns of children with DS were compared to those of intellectually average children with phonological disorder whose errors were characterized by inconsistency. The groups were matched for percentages of consonants produced in error. The data revealed no differences between the groups in terms of the number of words which were produced inconsistently on repeated productions in a picture-naming task. However, further analyses revealed differences in the type of errors made by the groups in that the children with phonological disorder characterized by inconsistent errors made more changes to words on repeated production than the group with DS. The deficits underlying inconsistent pronunciation of words in the two groups of children under investigation would appear to differ. Intervention strategies should target the deficits identified.