Quality control requires the definition of a quality standard, followed by quality documentation and comparison. In the case of deviation from the standard, the first step in quality assurance is the search for the reasons. After identification of weak points, strategies for quality improvement must then be developed and implemented. With prehospital trauma care as an example, a practical model of quality assurance is presented. Data analysis was performed using the prospective database of 8792 trauma patients who received prehospital trauma care in Cologne from 1. 1. 87 to 31. 12. 90. The Trauma Score was used for classification of the severity of injury. The quality standard in prehospital treatment of severely injured patients is defined as institution of an intravenous line, early intubation and transportation to a trauma centre. The time at the scene of the accident should not exceed 31 min. Among the 8792 trauma patients, 834 had severe injuries, defined as a Trauma Score equal to or less than 12 or a Glasgow Coma Scale equal to or less than 7. An intravenous line was started in 91.6%, early intubation was performed in 82.7%, and transportation to a trauma centre was realized in 62.5% of the patients. The average time at the scene was 34 min. Obviously the standard was not always achieved. Reasons for deviation from the standard are discussed. The fascinating aspect of the model proposed is that it enables quality assurance of prehospital treatment without recourse to hospital data.