Background: The purpose of this study is to determine the impact of negative affect (defined in terms of lack of optimism, depressogenic attributional style, and hopelessness depression) on the quality of life of women with type 1 diabetes mellitus. Methods: Participants (n=177) completed either an online or paper questionnaire made available to members of Australian diabetes support groups. Measures of optimism, attributional style, hopelessness depression, disease-specific data, and diabetes-related quality of life were sought. Bivariate correlations informed the construction of a structural equation model. Results: Participants were 36.3±11.3 years old, with a disease duration of 18.4±11.2 years. Age and recent glycosylated hemoglobin readings were significant contextual variables in the model. All bivariate associations involving the components of negative affect were as hypothesized. That is, poorer quality of life was associated with a greater depressogenic attributional style, higher hopelessness depression, and lower optimism. The structural equation model demonstrated significant direct effects of depressogenic attributional style and hopelessness depression on quality of life, while (lack of) optimism contributed to quality of life indirectly by way of these variables. Conclusion: The recognition of negative affect presentations among patients, and an understanding of its relevance to diabetes-related quality of life, is a valuable tool for the practitioner.