Studies carried out to support the existence of a critical period for language acquisition have concentrated mainly on the case of being in total deprivation from language contact, and in particular deprivation from auditory input in the entire time span before puberty. While arguing for a useful distinction between early and late critical periods, we attempt to investigate the written language production of a profoundly deaf young woman, here referred to as Maryam, who has missed the early years, before her official education as a deaf person began at the age of 54 months. During the study, several texts that we asked her to write were analysed. In addition, we held a test in which she was required to set disordered sentences in the right order. The results of text analysis indicated that despite her ability to communicate through written Persian, a considerable number of syntactically and morphologically ill-formed structures were observed in the texts she produced. While confirming the idea that some aspects of language, such as syntax and morphology, are affected much more than semantics and vocabulary, the existence of these deficits seems to strengthen the importance of early years in acquiring a language. (Contains 1 table and 1 figure.)