Healthy employee sleep is important for occupational safety, but the mechanisms that explain the relationships among sleep and safety-related behaviors remain unknown. We draw from Crain, Brossoit, and Fisher's (in press) work, nonwork, and sleep (WNS) framework and Barnes' (2012) model of sleep and self-regulation in organizations to investigate the influence of construction workers' self-reported sleep quantity (i.e., duration) and quality (i.e., feeling well-rest upon awakening, ability to fall asleep and remain asleep) on workplace cognitive failures (i.e., lapses in attention, memory, and action at work) and subsequent workplace safety behaviors (i.e., safety compliance and safety participation) and reports of minor injuries. Construction workers from two public works agencies completed surveys at baseline, 6 months, and 12 months. Our results suggest that workers with more insomnia symptoms on average reported engaging in fewer required and voluntary safety behaviors and were at a greater risk for workplace injuries. These effects were mediated by workplace cognitive failures. In addition, workers with greater sleep insufficiency on average reported lower safety compliance, but this effect was not mediated by workplace cognitive failures. These results have implications for future workplace interventions, suggesting that organizations striving to improve safety should prioritize interventions that will reduce workers' insomnia symptoms and improve their ability to quickly fall asleep and stay asleep throughout the night. (PsycINFO Database Record (c) 2019 APA, all rights reserved).