OBJECTIVE This study examined the usefulness of the Nonword Repetition Test (NRT; C. Dollaghan & T. F. Campbell, 1998) with 4-year-old children and the relationship among the NRT, language, and other aspects of mental processing. METHODS The NRT was administered to 64 children at 4 years of age; 44 had a history of typical language development (HTD), and 20 had a history of language delay (HLD) at 16 months of age. Study 1 compared methods of scoring phoneme errors to determine whether the NRT was appropriate for this age group. Study 2 examined whether the NRT differentiated HTD from HLD. Study 3 examined the relations among scores on the NRT and standardized tests of language and mental processing. RESULTS The NRT was found to be appropriate for 4-year-old children. Although all children had normal language abilities at the time of the study, the NRT (and several aspects of language and mental processing) differentiated between HTD and HLD. Relations among the NRT and other measures of language and mental processing were different from those previously reported, an unexpected finding that is inconsistent with traditional accounts of working memory and its relation to language development. Potential explanations are explored, and some directions for future research are suggested.