Work Stressors, Perseverative Cognition and Objective Sleep Quality: A Longitudinal Study among Dutch Helicopter Emergency Medical Service (HEMS) Pilots: Mirjam RADSTAAK, et al . Behavioural Science Institute, Radboud University Nijmegen, The Netherlands— Objectives This longitudinal study examined the associations between work stressors, perseverative cognition and subjective and objective sleep quality. We hypothesized work stressors to be associated with (i) poor nocturnal sleep quality and (ii) higher levels of perseverative cognition during a free evening. We further hypothesized (iii) perseverative cognition to be associated with poor nocturnal sleep quality and (iv) the association between work stressors and sleep quality to be mediated by perseverative cognition. Methods The participants were 24 pilots working for the Dutch Helicopter Emergency Medical Service (HEMS). They completed six questionnaires: at the end of three consecutive day shifts and each morning following the shifts. The questionnaires addressed work stressors (workload, distressing shifts and work‐related conflicts), subjective sleep quality and perseverative cognition. Participants wore actigraphs to assess sleep onset latency, total sleep time and number of awakenings. Results Correlation analysis revealed that (i) distressing shifts were related to delayed sleep onset ( r =0.50, p =0.026) and that workload was related to impaired sleep quality (e.g., subjective sleep quality: r =−0.42, p =0.044). Moreover, (ii) distressing shifts were positively related to perseverative cognition ( r =0.62, p =0.002), (iii) perseverative cognition delayed sleep onset ( r =0.74, p <0.001) and (iv) mediated the association between distressing shifts and sleep onset latency. Conclusions Perseverative cognition may be an explanatory mechanism in the association between work stressors and poor sleep.