Title: Relationships among coping, comorbidity and stress in patients having haemodialysis.Aim: This paper is a report of a study to examine relationships among stress, coping and comorbidity and test the interaction effect of comorbidity.Background: Haemodialysis imposes a variety of physical and psychosocial stressors that challenge patients. Comorbidity is a risk factor for many health outcomes. Research on how comorbidity influences the relationship between coping and stress is limited.Method: In this cross-sectional study, conducted from October 2002 to January 2003, 2642 patients, who had been having haemodialysis for at least 3 months, were interviewed by nursing managers in the 27 participating centres. The Haemodialysis Stressor Scale measured stressors and the Jalowiec Coping Scale were used to measure coping strategies. Hierarchical regression was used to analyse the data.Results: Haemodialysis patients with comorbidities were found to have higher levels of stress. Comorbidity had a moderating effect between choice of problem-oriented responses and isolated thoughts as coping strategies. These findings show that haemodialysis patients with comorbidities often choose positive coping strategies.Conclusion: Comorbidity not only has a direct impact on stress but also has a moderating effect on the relationship between coping and stress. Comorbidity may hold the key to healthcare professionals’ understanding of why patients having haemodialysis perceive different levels of stress and use various coping strategies. A personalized programme may be needed for each patient based on their different levels of comorbidity.