SummaryThree children with XXYY chromosome anomalies whose initial presenting symptom in speech therapy clinic was lack of a phonological system, are studied developmentally, psychologically and socially. Speech and language development are looked at in detail. Similarities and differences in their psycholinguistic abilities are discussed. Speech therapy methods are described. It is concluded that the laying down of kinaesthetic patterns is essential for the development of a phonological system in such children.