Purpose: (1) To investigate the prevalence of poor sleep quality and (2) to explore the associations between clinical, cognitive, and emotional factors and quality of sleep in patients with chronic widespread pain (CWP) receiving multidisciplinary treatment. Method: Baseline data were used from 163 patients with CWP referred for multidisciplinary treatment. Linear regression models were used to assess the relationship of clinical (pain, fatigue, pain interference, and disability), emotional (anxiety, depression, and psychological distress), and cognitive factors (catastrophizing, acceptance, self-efficacy, kinesiophobia and illness beliefs) with sleep quality, as measured using the Pittsburgh Sleep Quality Index. Results: Poor sleep quality was found in 92% of the patients. The multivariable model showed that a higher level of fatigue (b = 1.77, standard error [SE] = 0.62, β = 0.21, t = 2.87, P < 0.01), psychological distress (b = 0.02, SE = 0.01, β = 0.27, t = 3.50, P < 0.01), and more concerns about the illness (b = 0.46, SE = 0.18, β = 0.20, t = 2.57, P = 0.01) were independently associated with poorer quality of sleep. The overall linear regression model explains 27.9% of sleep quality. Conclusions: The high prevalence of poor sleep quality in patients with CWP referred for multidisciplinary treatment emphasizes the need to target sleep during treatment. Further research is needed to disentangle the cause–effect relationship between fatigue, psychological distress, and concerns about the illness and poor sleep (note: this abstract has been published before [Ann Rheum Dis. 2018;77:A1788]).