AIMS AND OBJECTIVES:To examine the association between subthreshold depression and self-care behaviours in adults with type 2 diabetes (T2D) attending a tertiary healthcare service. BACKGROUND:Diabetes is a global public health problem. Self-care behaviours are a fundamental element in managing diabetes as adherence to self-care activities is associated with improved glycaemic control. Depression in T2D is associated with decreased adherence to self-care behaviours. Adults with subthreshold depression in diabetes may have difficulties in achieving metabolic control. Further, people with subthreshold depression have an increased risk of developing major depression. Few studies have examined the association between subthreshold depression and self-care behaviours. DESIGN:A cross-sectional study. METHODS:The study will be conducted among 384 adults diagnosed with T2D for at least a year attending their routine outpatient appointment at Tribhuvan University Teaching Hospital in Nepal. Convenience sampling will be used to recruit study participants. Data will be collected via face-to-face interviews and a medical record review. Self-care behaviours will be assessed using the Summary of Diabetes Self-care activities and subthreshold depression will be determined using the Patient Health Questionnaire- 9. Covariates in the study include sociodemographic and clinical factors, diabetes knowledge, perceived social support and self-efficacy. This paper complies with the STROBE reporting guideline for cross-sectional studies. RESULTS:We will use multiple linear regression to examine the association between subthreshold depression and each self-care behaviours (i.e. diet, physical activity, foot care, blood glucose testing and medication) and total self-care behaviour. CONCLUSIONS:Effective management of diabetes requires adherence to self-care behaviours. The findings of the study will help in identifying an effective way to improve diabetes self-care. RELEVANCE TO CLINICAL PRACTICE:Our observations will inform nursing research and practice by providing evidence about how subthreshold depression may influence self-care behaviours.