Many commonly available trauma scores predict mortality, but to evaluate the success of a certain therapy or for difficult scientific and epidemiological purposes this may be insufficient in the face of improved survival rates. For outcome analysis of multiple trauma patients, the extent of medical resources needed could be an additional outcome measurement. McPeek et al. developed a potential scoring system for elective surgery patients, which was recently modified for multiple trauma patients. The current study investigated if the McPeek score could be prospectively used in multiple trauma patients and whether it could become an additional helpful tool in outcome assessment. Applicability was assessed by practical examples. In this prospective single-centre study at the University Hospital of Innsbruck, Austria, between December 2008 and November 2010 multiple trauma patients (≥ 18 years) with an injury severity score (ISS) ≥ 17 were enrolled. Besides demographic data, prehospital vital parameters and diagnoses, all diagnoses from the trauma, mortality, length of stay in the intensive care unit and the hospital were recorded. The commonly used trauma scores ISS, revised trauma score (RTS), a severity characterization of trauma (ASCOT) and trauma and injury severity score (TRISS) were applied and an observed McPeek score was allocated following end of hospitalization. The McPeek scoring system was used according to the latest modifications. A correlation between trauma scores and the McPeek score was performed. The McPeek score was then predicted by a common trauma score using ordinal regression with the polytomous universal model (PLUM method). By subtracting the predicted from the observed McPeek scores the residual McPeek value was calculated and used for practical examples of outcome analysis with the McPeek scoring system. Out of 406 identified multiple trauma patients during the study phase, 183 had to be excluded due to missing data (mainly prehospital or following transfer). A total of 223 patients (mean ISS 31.2, mean age 47.2 years) were enrolled and assigned to the population-based observed McPeek score (median 4.0). Correlation coefficients were Glasgow coma scale (GCS) 0.59, ISS 0.62, RTS 0.65, TRISS 0.74 and ASCOT 0.77 (p < 0.0001). The TRISS predicted the McPeek score best in ordinal regression (pseudo-R(2) = 0.944, p < 0.0001). The residual McPeek score (observed minus predicted) was used to illustrate the influence of the blood glucose level on admission and the influence of head injury on outcome of multiple injury patients in detail. The modified McPeek score is applicable to multiple trauma patients to assess outcome for scientific or epidemiological purposes. Its main advantage is that it quantifies outcome independently of regional or national circumstances.