Little research has addressed the relative influence of genetic and environmental factors on subclinical levels of anxiety in children. Of the two twin studies to date, one concluded that measures of adolescents' self-reported trait anxiety were best explained by shared environmental factors (Thapar & McGuffin, 1995), while the second determined that approximately half the variance was attributable to genetic effects (Topolski et al., 1997). The present study, using a sample of 547 twin pairs, reached conclusions similar to those of Topolski et al. Heritability was estimated at 45%. Measures of state anxiety conformed more closely to Thapar and McGuffin's findings, with environmental factors accounting for the variance.