Background: The comorbidity of acute coronary syndrome and diabetes affects patient prognoses. Therefore, it is important to manage these diseases simultaneously. Purpose: In this study, the effect of nursing counseling on treatment compliance was investigated in patients who had received surgical treatment for acute coronary syndrome and had been recently diagnosed with diabetes. Methods: A quasi-experimental design with pretest-posttest control group was used. The study sample consisted of 60 patients (intervention group = 30, control group = 30). The data were collected using a patient information form, the Patient Learning Needs Scale, and the Scale for Patient Compliance with Type 2 Diabetes Mellitus Treatment. This study was conducted in compliance with the Transparent Reporting of Evaluations with Nonrandomized Designs checklist. Results: The intervention group earned significantly higher posttest scores on the Patient Learning Needs total scale and subscales than the control group.Moreover, intervention group compliance with treatment was higher than that of the control group. Furthermore, although significant improvements were found in the average posttest body mass index, fasting blood glucose, HbA1c, total cholesterol, triglyceride, and low-density lipoprotein cholesterol values of the control group, the between- group differences in these values were not significant. Conclusions/Implications for Practice: It is important for nurses to provide counseling services that align with the learning needs of their patients. Also, nursing counseling units should be created and staffed by both specialist nurses and nurse trainers working in healthcare institutions.