In the present study, language development of Dutch children with a cochlear implant (CI) in a bilingual educational setting and Flemish children with a CI in a dominantly monolingual educational setting is compared. In addition, we compared the development of spoken language with the development of sign language in Dutch children. Eighteen children with a CI participated in the study: six Dutch children older than 18 months at implantation and 12 Flemish children, of whom seven were younger than 18 months at implantation and five were older than 18 months. Tests were administered on auditory perception, speech intelligibility, spoken language and sign language (Dutch children). Five assessments were made to monitor language development of the children: a pre-test before implantation and four post-tests at six, 12, 24 and 36 months after implantation. In general, Flemish children showed more progress in spoken language development than Dutch children. Moreover, earlier implanted Flemish children showed more progress than later implanted Flemish children. This applies to auditory perception, speech intelligibility and spoken language. Whereas spoken language of Dutch children improved in the course of time, the development of sign language in Dutch children did not show any progress. Despite possible alternative explanations, such as better residual aided hearing before implantation or more professional support, it is plausible that the differences are partly caused by the linguistic environment. The lack of progress in development of sign language might be explained by the decreasing use of sign language by parents after implantation. (Contains 1 table and 5 figures.)