Background: In adults, the appearance of nucleated red blood cells (NRBC) in the peripheral blood is associated with several severe diseases. When NRBC are detected in the blood, the prognosis is poor. The purpose of this study was to identify the impact of NRBC on the clinical outcomes of surgical intensive care patients under consideration of established risk models., Methods: In a prospective study, the detection of NRBC in the peripheral blood of surgical intensive care patients was analyzed with regard to the in- hospital mortality. NRBC were daily measured with a Sysmex XE-2100. The prognostic significance of NRBC in blood was analyzed under consideration of established risk scores for intensive care patients, i.e., the Acute Physiology and Chronic Health Evaluation (APACHE II) and the Simplified Acute Physiology Score (SAPS II)., Results: Two hundred seventy-one surgical intensive care patients were included in this study. The mean age was 61.3 years +/- 1.2 years (range, 18-98 years). The average APACHE II and SAPS II scores were 20.6 +/- 0.6 and 44.1 +/- 1.2, respectively. The in-hospital mortality of NRBC-positive patients was 51.7% (45 of 87). This was significantly higher (p < 0.001) than the mortality of NRBC-negative patients (12.0%, 22 of 184). The area under curve (C-statistic) was 0.77. Mortality increased with the NRBC concentration. On average, in NRBC-positive patients who died, NRBC were detected for the first time 13.3 days +/- 3.1 days (n = 45, median = 6 days) before death. Multiple logistic regression analysis under consideration of the APACHE II or the SAPS II revealed a significant association between NRBC and increased mortality, the mean odds ratio being 1.97 for each increase in the NRBC category (0/microL; 1-40/microL; 41-80/microL; 81-240/microL, >240/microL). In contrast, under consideration of the NRBC-data the mean odds ratios for the increase of one score point of the APACHE II and SAPS II were 1.10 and 1.05, respectively. Therefore, each step-up in the NRBC category is equivalent to approximately 7 APACHE II-score points and 14 SAPS II-score points, respectively., Conclusions: The daily screening for NRBC in blood of surgical intensive care patients is of prognostic power with regard to the patients' in-hospital mortality. This prognostic significance of NRBC was independent of the scores APACHE II and SAPS II, respectively. Therefore, for prognostic purposes an adjustment of these established risk models by including the NRBC-results is feasible.