Insomnia co-occurs with smoking. However, mechanisms that may explain their comorbidity are not well known. The present study tested the hypothesis that insomnia would exert an indirect effect on negative reinforcement smoking processes via emotion dysregulation among 126 adult daily smokers (55 females; Mage = 44.1 years, SD = 9.72). Dependent variables included negative reinforcement smoking outcome expectancies, negative reinforcement smoking motives, and two negative expectancies from brief smoking abstinence (somatic symptoms and harmful consequences). Insomnia symptoms yielded a significant indirect effect through emotion dysregulation for negative reinforcement smoking outcome expectancies, negative reinforcement smoking motives, and harmful consequences expectancies from brief smoking abstinence. In contrast to prediction, however, insomnia was not associated with somatic symptom expectancies from brief smoking abstinence through emotion dysregulation. These data may suggest that the indirect effect of emotion dysregulation is more relevant to cognitive-affective negative reinforcement processes rather than somatic states. Overall, the present findings contribute to a growing body of literature linking emotion dysregulation as an explanatory mechanism for insomnia and smoking and uniquely extend such work to an array of clinically significant negative reinforcement smoking processes.Psychology, Department o