Prehospital care delivered by multiple agencies and their paramedics in a suburban emergency medical services (EMS) system was compared to assess the impact of a receiving hospital quality assurance audit on paramedic and agency performance. A committee of physicians, nurses, and paramedics developed performance criteria based on a county EMS protocol. Run tapes were reviewed to assess accuracy of runsheets. Deviations were categorized and tabulated with Lotus 1-2-3 software. A profile was developed for each agency and paramedic. Results were returned to supervisors of each agency on an intermittent basis with subsequent feedback to paramedics. Four agencies and 100 paramedics were audited during the 18-month study period, with a total of 2,406 runsheets reviewed. Average deficiencies per run per quarter for all paramedics decreased from 0.47 to 0.34 (P less than .006). For one agency, deficiencies per run declined from 1.98 to 1.06, although this was not statistically significant (P = .068). During the second nine-month segment of the study, the records of 62 paramedics were reviewed. A mean deficiency per run of 0.39 +/- 0.55 was found, with four paramedics performing more than two standard deviations from the mean. This receiving hospital EMS quality assurance audit has helped document problems in agency procedure performance and individual paramedic performance. It also has improved compliance with county protocol on patients delivered to our institution.