Objective:To compare procalcitonin (PCT) plasma levels of injured patients with the incidence and severity of systemic inflammatory response syndrome (SIRS), infection, and multiple organ dysfunction syndrome (MODS) and to assess the predictive value of PCT for these posttraumatic complications.Design:Retrospective study comparing patients with mechanical trauma in terms of severity of injury, development of infectious complications, and organ dysfunctions.Setting:Level I trauma center with emergency room, intensive care unit, and research laboratory.Patients:Four hundred five injured patients with an Injury Severity Score of ≥9 points were enrolled in this study from January 1994 to February 1996.Interventions:Blood samples were collected on the day of admission and on days 1, 3, 5, 7, 10, 14, and 21 thereafter.Measurements and Main Results:We determined PCT serum levels using a specific immunoluminometric assay. We retrospectively evaluated the occurrence of SIRS, sepsis, and MODS using patients' charts. Mechanical trauma led to increased PCT plasma levels dependent on the severity of injury, with peak values on days 1 and 3 (p< .05) and a continuous decrease within 21 days after trauma. Patients who developed SIRS demonstrated a significant (p< .05) increase of peak PCT plasma levels compared with patients without SIRS. The highest PCT plasma concentrations early after injury were observed in patients with sepsis (6.9 ± 2.5 ng/mL; day 1) or severe MODS (5.7 ± 2.2 ng/mL; day 1) with a sustained increase (p< .05) for 14 days compared with patients with an uneventful posttraumatic course (1.1 ± 0.2 ng/mL). Moreover, these increased PCT plasma levels during the first 3 days after trauma predicted (p< .0001; logistic regression analysis) severe SIRS, sepsis, and MODS.Conclusions:These data indicate that PCT represents a sensitive and predictive indicator of sepsis and severe MODS in injured patients. Routine analysis of PCT levels seems to aid early recognition of these posttraumatic complications. Thus, PCT may represent a useful marker to monitor the inflammatory status of injured patients at risk.