Li YI, et al. - Data from Waves I, II, and IV of the National Longitudinal Study of Adolescent to Adult Health was utilized to examine insomnia as a mediator in the longitudinal relationship between anxiety and subsequent depression. As per structural equation modeling, the relationship between anxiety and subsequent depression seemed significantly mediated by insomnia and unrestful sleep. Anxiety might be increasing the risk for the development of later depression via insomnia.