OBJECTIVE: Our aim in this study was to show the relationship between long-term all-cause mortality and thyroid functions in the elderly patient group that underwent primary percuta-neous coronary intervention with the diagnosis of ST-segment elevation myocardial infarction. METHODS: Two-hundred seventy patients over 65 years of age who underwent primary percutaneous coronary intervention with the diagnosis of ST-segment elevation myocardial infarction were analyzed retrospectively. After applying the exclusion criteria, 198 patients were included in the study. The patients were divided into 2 groups according to their out-of-hospital mortality status. Angiographic, laboratory, echocardiographic, and electrocardiographic data were analyzed. RESULTS: The mean age of 198 patients in the study was 72.5 ± 6.6 years, and the median follow-up time was 101.7 months. Age was higher in the deceased group (70.4 ± 5.4 vs. 74.5 ± 6.9, P < 0.001). In multivariate analysis, age (odds ratio: 1.59, P = 0.003), insulin (odds ratio: 2.561, P = 0.016), angina balloon time (odds ratio: 1.134, P = 0.002), number of serious stenoses (odds ratio: 1.702, P = 0.003), creatinine (odds ratio: 3.043, P < 0.001), and fT4 (odds ratio: 2.026, P = 0.026) were determined as independent predictors of mortality. The fT4 level was correlated with the uric acid level (R: 0.182, P = 0.02) and the fT3 level was correlated with albumin (R: -0.253, P = 0.001) and creatinine (R: -0.224, P = 0.003) levels. A fT4 level cutoﬀ value of 0.99 ng/mL had a sensitivity of 76%, a speciﬁcity of 54%, and an area under the curve of 0.675 in predicting mortality. In Kaplan-Meier analysis, fT4 elevation was strongly associated with mortality (P = 0.01). CONCLUSION: In our study, subclinical values in thyroid functions were found to be associated with increased mortality, apart from known factors in elderly patients who underwent primary PTCA with the diagnosis of ST-segment elevation myocardial infarction.