Objective To examine whether moderate to severe congenital hearing loss (MSCHL) leads to persistent morphosyntactic problems in the written language production of adults, as it does in their spoken language production. Design Samples of written language in Dutch were analysed for morphosyntactic correctness and syntactic complexity. Study sample 20 adults with MSCHL and 10 adults with normal hearing (NH). Results Adults with MSCHL did not differ from adults with NH in the morphosyntactic correctness and syntactic complexity of their written utterances. Within the MSCHL group, the number of morphosyntactic errors in writing was related to the degree of hearing loss in childhood. Conclusions At the group level, MSCHL does not affect the morphosyntactic correctness of language produced in the written modality, in contrast to earlier observed effects on spoken language production. However, at the individual level, our data suggest that adults who acquired their language with more severe auditory limitations are more at risk of persistent problems with morphosyntax in written language production than adults with a lower degree of hearing loss in childhood.