Sleep disturbances are common in posttraumatic stress disorder (PTSD) and can have major impacts on workplace performance and functioning. Although effects between PTSD and sleep broadly have been documented, little work has tested their day-to-day temporal relationship particularly in those exposed to occupational trauma. The present study examined daily, bidirectional associations between PTSD symptoms and self-reported sleep duration and quality in World Trade Center (WTC) responders oversampled for PTSD. WTC responders (N = 202; 19.3% with current PTSD diagnosis) were recruited from the Long Island site of the WTC health program. Participants were administered the Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV; SCID; First, Spitzer, Gibbon, & Williams, 1997) and completed daily assessments of PTSD symptoms, sleep duration and sleep quality for 7 days. PTSD symptoms on a given day were prospectively associated with shorter sleep duration (β = -.13) and worse sleep quality (β = -.18) later that night. Reverse effects were also significant but smaller, with reduced sleep duration (not quality) predicting increased PTSD the next day (β = -.04). Effects of PTSD on sleep duration and quality were driven by numbing symptoms, whereas effects of sleep duration on PTSD were largely based on intrusion symptoms. PTSD symptoms and sleep have bidirectional associations that occur on a daily basis, representing potential targets to disrupt maintenance of each. Improving PTSD numbing symptoms may improve sleep, and increasing sleep duration may improve intrusion symptoms in individuals with exposure to work-related traumatic events. (PsycINFO Database Record (c) 2019 APA, all rights reserved).