Purpose: This study tested the accuracy with which the MacArthur-Bates Communicative Development Inventories, Level III (CDI-III), a parent report measure of language ability, discriminated children with language impairment from those developing language typically. Method: Parents of 58 children, 49 with typically developing language (age 30 to 42 months) and 9 with language impairment (age 31 to 45 months) completed the CDI-III, a 2-page questionnaire that includes 100 vocabulary items, 12 sentence pairs, and 12 questions regarding linguistic concepts. Results: A discriminant analysis indicated that the CDI-III total score together with age classified children into language status groups with 96.6% accuracy overall. The corresponding likelihood ratios supported this strong level of accuracy, although precision may not be as high as indicated by broad confidence intervals. Conclusions: Results of this study contribute to the accumulating evidence on the types of valid inferences that may be made from the CDI-III, specifically its classification accuracy. Further research should continue to investigate classification accuracy in larger samples with broader maternal education levels and with different types of language impairments. Additional research should also investigate the classification accuracy when the CDI-III is used in combination with other tests. (Contains 3 tables, 1 figure, and 7 footnotes.)