SUMMARYNine children suffering from Landau‐Kleffner syndrome and 25 children with developmental expressive disorder were tested for comprehension of the grammatical structure of English in spoken, written and signed (Paget‐Gorman) language modalities. It is shown that the comprehension problems of children with Landau‐Kleffner syndrome are not restricted to spoken language, but are also found when written or signed language is used. Further, in all three language modalities these children show deviant patterns of comprehension consistent with the notion that they treat language as having a sequential rather than a hierarchical structure. However, similar patterns of performance are found in profoundly deaf children, indicating that peripheral auditory deprivation is a sufficient condition for these deviant patterns of comprehension to de