OBJECTIVES: Troponin T levels (Tn) are good predictors of outcome in patients with acute coronary síndromes without ST-segment elevation (ACS). Diabetic patients have demonstrated to carry a worse prognosis than non-diabetics after having an ACS. METHODS: Tn were determined in 346 patients (227 men, average age 67.6 years) admitted to hospital after an acute chest pain episode which was diagnosed as ACS. Plasma sampling of Tn was made 6 to 24 hours after the clinical episode. Ninety patients (26%) had diabetes mellitus (D+). Personal or phone interview of patients or relatives were obtained three months after the acute episode asking for endpoints as death, myocardial infarction (MI) or NYHA III or IV heart failure (HF). RESULTS: Twenty (22.2%) of all D+ patients had death, MI or HF (RR = 2.7 against D-; 95% CI = 1.3-5.6; p = 0.008). Tn was equal or higher than 0.1 ng/ml in 133 patients (Tn+ group) and lower than 0.1 ng/ml in the other 213 patients (Tn- group). Twenty-eight Tn+ patients (21.1%) had death, MI or HF (RR = 2.8 against T-; 95% CI = 1.6-5.0; p <0.001). When age, sex and ST segment changes were also included in a logistic regresión, D and Tn remained as the only independent predictors of outcome. Tn+ lost its predictive ability in non diabetics (RR = 1.2 against T-; IC 95% = 0.4-3.9; p = 0.77) and increased it in diabetics (RR = 7.9; IC 95% =1.5-41.0; p = 0.014). In the groups D-T- and D+T+ the percentage of combinated outcome were 7.0% and 32,7%, respectively. CONCLUSIONS: diabetes and Tn are independent predictors of outcome in the first three months after an acute coronary syndrome without ST segment elevation. Their predictive ability is additive, so that diabetics with elevated Tn have five times the risk of non-diabetics with low Tn. The ability of Tn to predict major events seems to be lost in non-diabetic patients.