INTRODUCTION: Clinical depression is a known consequence of acute coronary syndrome (ACS) and is associated with an adverse outcome among these patients, although this is often under-recognised. Through this study, we investigated the incidence of depression in post-ACS patients and its associated factors. METHODS: We conducted a prospective cohort study in 95 patients with ACS admitted to University Malaya Medical Centre, Malaysia. Clinical depression was assessed during the index admission and at 30 days after discharge, using the Patient Health Questionnaire-9 (PHQ-9). Data was analysed using IBM SPSS Statistics, and binary logistic regression was used to determine the independent factors associated with depression, after adjusting for significant demographic variables and clinical characteristics. The strength of this association was presented as odds ratio and 95% confidence interval, and the significance level was set at 0.05. RESULTS: The mean age of the study population was about 60 years, and 72.6% of the patients were male. Symptoms of depression were present in 88.4% of the patients at baseline. Depression at 30 days was more likely in female patients, patients with diabetes mellitus and patients on dialysis (p = 0.024, p < 0.001, p = 0.008, respectively). Patients with baseline moderate to severe depression were more likely to have moderate to severe depression at 30 days (p < 0.001). Baseline depression was the strongest predictor of depression at 30 days. An increment of one unit in PHQ-9 baseline score increased the risk of developing severe depression at 30 days by 31%. CONCLUSION Depression was prevalent in our post-ACS patients. The associated factors were female gender, diabetes mellitus and dialysis treatment.