int. j. lang. comm. dis., 2000, vol. 35, no. 2, 165–188 Prevalence and natural history of primary speech and language delay: ndings from a systematic review of the literature James Law †* , James Boyle ‡ , Frances Harris † , Avril Harkness ‡ and Chad Nye § † Department of Language and Communication Science, City University, London, UK ‡ Department of Psychology, University of Strathclyde § Department of Communication Disorders, University of Central Florida ( Received July 1998; accepted March 1999 ) Abstract The prevalence and the natural history of primary speech and language delays were two of four domains covered in a systematic review of the literature related to screening for speech and language delay carried out for the NHS in the UK. The structure and process of the full literature review is introduced and criteria for inclusion in the two domains are specied. The resulting data set gave 16 prevalence estimates generated from 21 publications and 12 natural history studies generated from 18 publications. Results are summarized for six subdivisions of primary speech and language delays: (1) speech and/or language, (2) language only, (3) speech only, (4) expression with comprehension, (5) expression only and (6) comprehension only. Combination of the data suggests that both concurrent and predictive case denition can be problematic. Prediction improves if language is taken independently of speech and if express- ive and receptive language are taken together. The results are discussed in terms of the need to develop a model of prevalence based on risk of subsequent diYculties. Keywords : primary speech and language delay, children, prevalence, natural history, epidemiology. Introduction The present review was commissioned and managed by the National Health Service Centre for Reviews and Dissemination at the University of York on behalf of the *Address correspondence to: James Law, Department of Language and Communication Science, City University, Northampton Square, London EC1V OHB, UK; e-mail: J.C.Law@city.ac.uk International Journal of Language & Communication Disorders ISSN 1368-2822 print/ISSN 1460-6984 online © 2000 Royal College of Speech & Language Therapists http://www.tandf.co.uk/journals/tf/13682822.html