Purpose: We asked whether sentence repetition accuracy could be explained by interactions of participant processing limitations with the structures of the sentences. We also tested a prediction of the procedural deficit hypothesis (Ullman & Pierpont, 2005) that adjuncts are more difficult than arguments for individuals with developmental language impairment (DLI). Method: Forty-four young adults participated, 21 with DLI. The sentence repetition task varied sentence length and the use of arguments and adjuncts. We also administered measures of working memory and processing speed. Our regression models focused on these interactions: group and argument status; processing speed, length, and argument status; and working memory capacity, length, and argument status. Results: Language ability group was a significant predictor of sentence repetition accuracy but did not interact with argument status. Processing speed interacted with sentence length and argument status. Working memory capacity and its separate interactions with argument status and sentence length predicted sentence repetition accuracy. Conclusions: Many adults with DLI may have difficulty with adjuncts as a result of their working memory limitations rather than their language ability. Cognitive limitations common to individuals with DLI are revealed more by particular sentence structures, suggesting ways to construct more diagnostically accurate sentence repetition tasks.