Adherence to the treatment of type 2 diabetes (T2D), which includes the use of prescribed drugs, following a healthy diet, and adopting a physically active lifestyle, is important to control the disease and improve the patients’ quality of life. The present study aimed to explain the determinants of adherence to treatment in patients with T2D based on Pender’s Health Promotion Model (HPM). The present research used a qualitative content analysis and was based on Pender’s HPM. The data were collected through in-depth semi-structured interviews with 20 T2D patients using a purposive sampling in Bandar Abbas, southern Iran. Maximum variation was considered in terms of gender, age, history of diabetes, type of drug used, education, and occupation. The data collection continued until data saturation. At the same time, the collected data were analyzed using the directed content analysis. MAXQDA 10 was used to manage codes and facilitate data analysis. The data analysis led to the extraction of 10 categories and 19 subcategories as the determinants of adherence to the treatment of T2D patients. The participants shared their experiences about personal characteristics and their ecological environment, specific cognition and emotions, and the behavioral results and experience as the determinants of adherence to T2D treatment. The categories extracted from this study in the form of HPM constructs provided a framework to explain treatment adherence. This information can help policy makers and planners in designing future programs.