Purpose: To examine whether Obstructive Sleep Apnoea severity, sleep-related problems, and anxiety are associated with work functioning in Obstructive Sleep Apnoea patients, when controlled for age, gender and type of occupation. To investigate whether anxiety moderates the associations between sleep-related problems and work functioning. Materials and methods: We included 105 Obstructive Sleep Apnoea patients (70% male; mean age 46.62 ± 9.79 years). All patients completed the Pittsburgh Sleep Quality Index, the Epworth Sleepiness Scale, the Beck Anxiety Inventory, and the Work Role Functioning Questionnaire-2.0. Results: Obstructive Sleep Apnoea-severity, poor nighttime sleep quality, and anxiety were univariately associated with impaired work functioning. Multivariate analyzes revealed that poor perceived sleep quality was more strongly associated with work functioning than sleep efficiency and daily disturbances. Anxiety was strongly associated with impaired work functioning. After adding anxiety, the explained variance in work functioning increased from 20% to 25%. Anxiety moderated the association between low and medium levels of nighttime sleep quality problems and work functioning. Conclusions: Poor perceived sleep quality and anxiety were strongly associated with impaired work functioning in Obstructive Sleep Apnoea patients. These findings may help to optimize management, standard treatment, and work functioning in people with Obstructive Sleep Apnoea when confirmed in longitudinal studies.Implications for RehabilitationStudies show an impairment of functional status, including work functioning, in obstructive sleep apnea patients.Aside from physical disorders, obstructive sleep apnea patients often experience mental problems, such as anxiety.As many people with obstructive sleep apnea are undiagnosed, our results demonstrate to employers and healthcare professionals the need to encourage patients for obstructive sleep apnea screening, especially in the situation of impaired work functioning, increased anxiety, and poor sleep quality.The associations between obstructive sleep apnea, sleep and anxiety might increase the awareness of health professionals towards optimizing diagnostic accuracy and standard treatment. Studies show an impairment of functional status, including work functioning, in obstructive sleep apnea patients. Aside from physical disorders, obstructive sleep apnea patients often experience mental problems, such as anxiety. As many people with obstructive sleep apnea are undiagnosed, our results demonstrate to employers and healthcare professionals the need to encourage patients for obstructive sleep apnea screening, especially in the situation of impaired work functioning, increased anxiety, and poor sleep quality. The associations between obstructive sleep apnea, sleep and anxiety might increase the awareness of health professionals towards optimizing diagnostic accuracy and standard treatment.