This paper concerns the relationship between French Sign Language (LSF) and written French skills developed by Deaf children. Previous studies showed positive correlations between ASL and written English skills, with little analysis of the processes involved. In the investigation presented here, thirty-nine bilingual Deaf children, aged from 8 to 17, from the French-speaking/signing part of Switzerland, were studied. Their comprehension and production skills were tested at the morphosyntactic and narrative levels. Results show positive correlations between the skills developed in written French and LSF. These data provide new evidence that early mastery of a natural sign language facilitates the acquisition of a written language. In addition, sign language narrative and comprehension skills appear to play an important role in this relationship.