The present present study investigated whether autonomic flexibility predicted future anxiety levels in adolescent boys and girls. This study is part of the TRacking Adolescents' Individual Lives Survey (TRAILS), a prospective cohort study of Dutch adolescents. The current study included a subsample of 965 individuals. Measures of autonomic flexibility, i.e., heart rate (HR) and respiratory sinus arrhythmia (RSA), were determined during the first assessment wave (T1: participants 10-12 years old). Self-reported anxiety was assessed at the first and second assessment wave (T2: participants 12-14 years old). Possible gender differences and co-occurring depressive problems were examined. In girls, low RSA predicted anxiety levels 2 years later. In boys, no associations between HR and RSA and future anxiety were found. We conclude that in adolescent girls from the general population, signs of reduced autonomic flexibility (i.e., low RSA) predict future anxiety levels. Since the effect size was small, at this point, RSA reactivity alone cannot be used to identify individuals at risk for anxiety, but should be regarded as one factor within a large group of risk factors. However, if the present findings are replicated in clinical studies, intervention programmes - in the future - aimed at normalising autonomic functioning may be helpful. (C) 2009 Elsevier Ireland Ltd. All rights reserved.