Background: Anxiety-related behaviors (ARBs) are commonly observed during typical development, yet few studies have investigated their etiology in middle childhood. This study aimed to examine both the phenotypic and genetic differentiation of ARB subtypes within the general population at age 7 and 9. It constituted a follow-up to an earlier study of ARBs in preschool children. Methods: We investigated the phenotypic structure of ARBs in a large population-based twin sample, comprising 7,834 twin pairs at age 7 and 3,644 twin pairs at age 9. Quantitative genetic modeling techniques were then used to determine the relative influences of genetic and environmental factors upon different types of ARB and upon the covariation between them. Results: Factor analysis supported the presence of five ARB factors at both ages: negative cognitions, negative affect, fear, obsessive–compulsive behaviors, and social anxiety. Multivariate genetic analyses revealed significant genetic effects and a small but significant influence of shared environment for all ARB subtypes. There was a moderate level of genetic specificity for each subtype as well as some shared genetic effects. Shared environmental influences correlated highly across all types of ARB, whereas nonshared environmental effects were largely subtype specific. Conclusions: The current results suggest that ARBs can be differentiated both phenotypically and genetically within middle childhood, with subtypes reflecting symptom groupings of diagnosable disorders but also aspects of temperament. Although some etiological risk factors lead to a generalized vulnerability to anxiety, others may serve to differentiate between different types of ARBs. Depression and Anxiety, 2009. © 2009 Wiley-Liss, Inc.