This article describes the development of new scales for assessing the status of a young child's language comprehension and production. Items and sections on the scales were included to reflect advances in research on language acquisition and impairment. The New Reynell Developmental Language Scales (NRDLS) were trialled on 301 children and then standardized on a sample of 1,266 participants across the age range 2;00-7;6 years. Evaluations of reliability (internal and test-retest) and concurrent validity were carried out and also discriminant validity was evaluated with a further small sample of children with primary language impairment. Results are reported and discussed. An illustrative example of how the NRDLS could be used is given, in which the performance of a typically developing child and that of a matched child with primary language impairment are compared.