BACKGROUND: Mortality rates of intensive care patients are quite high. The aim of this study was to determine the role, as well as to compare the value of several markers in predicting mortality in intensive care patients. Patient-wise, this is the largest study of its kind and the first that attempts to correlate the degree of thyroid hormone suppression with elevations in procalcitonin (PCT) levels. PATIENTS AND METHODS: In this study, a total of 417 patients were included in the final analysis, 235 of which were men (56%), and 182 were women (44%). Predictors of mortality that were investigated include age, APACHE II score, PCT, free triiodo-L-thyronine (fT3), free tetraiodothyronine/thyroxine (fT4) and thyroid stimulating hormone/thyrotropin (TSH). RESULTS: High APACHE II score and low PCT levels, as well as suppression of fT3, fT4 and TSH levels were all found to be associated with higher mortality in our intensive care patients (p < 0.001). Suppression of thyroid hormones was also found to be reciprocally correlated with high APACHE II scores and PCT levels (p < 0.05). CONCLUSION: Calculation of APACHE II score as well as measurement of PCT, fT3, fT4 and TSH levels may all be useful as predictors of mortality in intensive care patients.