Summary Insomnia is highly prevalent among military veterans, with rates nearly double that of civilian populations. Insomnia typically co-occurs with other psychological problems, including substance use (e.g. cannabis) and perceived stress. Much of the research focused on insomnia, stress and cannabis use explores cannabis as a sleep aid and a mechanism for stress relief. However, recent theoretical and empirical evidence suggests a dynamic interplay between insomnia, cannabis use and perceived stress, yet few longitudinal studies exist. Using a sample of 1105 post-9/11 veterans assessed over four time points across 12 months, we used latent difference score modelling to examine proportional change between insomnia, perceived stress...