INTRODUCTION : In the current literature, there is a well-established necessity for the improvement of bilingual language diagnostics. Nowadays, the majority of clinicians in Belgium still rely on standardized tests with monolingual norm samples. It is therefore fundamental to have a detailed knowledge of the performance of bilingual children on these monolingual normed tests. Furthermore, there is also a need for unambiguous longitudinal research on the language performances of bilingual children. Therefore, this study aims to investigate the language skills of 25 Turkish-Dutch successive bilinguals compared to 25 age- and gender-matched monolingual Dutch children. In 9 bilinguals and 13 monolinguals, longitudinal data of 3 years (at 6 years and at 9 years) were collected and compared. METHODS : The subject group consisted of 25 bilingual Turkish-Dutch children with a mean age of 9 years and 6 months (SD 0.26 years, min. 8 years and 11 months to max. 9 years and 10 months) with Turkish as the dominant home language. Language exposure to Dutch was at least 3 years. An age- and gender-matched control group of 25 monolingual Dutch children with same educational backgrounds was compiled. Language skills were investigated using the Dutch version of the CELF. In 22 children, language skills were reassessed 3 years later in a follow-up study. Data were compared using the Mann-Whitney U test and Wilcoxon matched-pairs signed-rank test. RESULTS : Language comprehension and production were significantly lower in the bilingual children compared to the monolinguals. After 3 years, the language delay in bilingual Turkish-Dutch children remained the same. Language production in the bilingual children was mainly influenced by the profession of the mother and the home language. CONCLUSION : The low performances of typically developing Turkish-Dutch children on language batteries are worrying and have clinical implications. The same language gap was found at the age of 6 and 9 years in Turkish-Dutch bilingual children compared to monolingual Dutch children, implying that the bilingual children did not catch up with their peers.