The purpose of this study was to investigate whether thyroid hormone levels have any predictive value for mortality in patients presenting to the emergency department with acute myocardial infarction (AMI). Three groups of patients admitted to the emergency department within the 11-month study period were considered eligible: 95 patients with chest pain and proven AMI, 26 patients with chest pain and no AMI, and 114 patients who served as controls with no evidence of any major disease. Cardiac enzymes and the following thyroid hormones were analyzed and compared between groups, regarding effects of historical and demographic factors: thyrotrophin, free triiodothyronine (FT3), total triiodothyronine (TT3), free thyroxine (FT4), and total thyroxine (TT4). Sixteen patients with AMI (16.8%) died within the study period. Troponin T and creatine kinase-B with an M-type subunit levels were significantly higher in the nonsurvivors when compared with survivors. Survivors in the AMI group had higher TT3, TT4, and lower FT4 levels, while the nonsurvivors in the AMI group had higher thyrotrophin and lower TT3, FT3 and FT4 levels than controls. In the AMI group, the nonsurvivors had lower TT3 and FT3 levels than the survivors. A history of diabetes mellitus and/or angina, TT3, or FT3 was an independent predictor of mortality. TT3 and FT3 appear to be independent prognostic factors in patients with AMI.