Background: To explore the relationships between serum procalcitonin (PCT) level, severity and different stresses of non-septic critically ill patients. Materials and Methods: Patients were divided into traumatic stress, stroke-induced stress and non-infectious inflammatory stress groups. According to 28-day prognosis, they were divided into survival and death groups. The factors affecting prognosis were studied by multivariate logistic regression analysis. Results: PCT level was significantly positively correlated with Acute Physiology and Chronic Health Evaluation II (APACHE II) and sequential organ failure assessment (SOFA) scores (P=0.001). The PCT level and abnormality rate of the traumatic stress group significantly exceeded those of other groups (P---lt---0.05). The APACHE II score, SOFA score and 28-day mortality rate of traumatic stress and stroke-induced stress groups significantly exceeded those of the non-infectious inflammatory stress group (P---lt---0.05). The PCT level, APACHE II score and SOFA score of the death group significantly surpassed those of the survival group (P---lt---0.05). With rising PCT level, APACHE II score, SOFA score and 28-day mortality rate all increased, with significant intergroup differences (P---lt---0.01). Multivariate logistic analysis showed that serum PCT level, APACHE II score and SOFA score were independent risk factors for prognosis. The area under ROC curve for prognosis evaluated by PCT level was 0.797 (95%CI = 0.710~0.878, P=0.000). At a 4.3 μg/L cut-off, the sensitivity and specificity for predicting 28-day mortality were 87.4% and 78.1%, respectively. Conclusion: The serum PCT level of non-septic critically ill patient was positively correlated with severity, which was more likely elevated by traumatic stress than other stresses.