The article constitutes a description of selected aspects of the development of linguistic knowledge of an eight-year-old hearing boy against the background of the process of his language development with deaf parents who communicate using sign language. The results of previous studies, mostly English-language, in terms of the impact of an unusual language environment on the speech and language development of hearing children of deaf parents, are not unambiguous. This publication describes one of several cases comprising the empirical material of broader research1 whose goal is, among others, the identification and description of the communicative and language competences (mainly in terms of phonological language) of hearing children of deaf parents.