The objective was to describe our experience with implementation of standing field treatment protocols (SFTP) in a large, urban EMS system. A prospective, consecutive observational study examining the first 21 days of implementation of SFTPs in the City of Los Angeles, California. SFTPs were developed for 7 medical chief complaints and all major trauma patients. There were 13,586 EMS incidents, of which 4,037 (30%) received ALS treatment. SFTPs were used on 2,177 of these incidents, representing 54% of all ALS runs and 16% of all EMS incidents. The most frequently used SFTPs were for altered level of consciousness (29%), and chest pain (25%). The most common errors found were failure to document reassessment of the patient after each medication administration (45% fallout rate), and failure to document and attach a copy of the ECG to the EMS report (40%). The mean fallout rate for failure to establish or attempt IV access, administer oxygen, or provide cardiac monitoring was 7%. Out of 1,450 incidents with outcome data provided by the receiving hospitals, only 3 cases (2%) involved incorrect treatment, with an additional 2 involving the unnecessary use of lidocaine. None of these instances resulted in adverse effects or complications. SFTPs were integrated into a large EMS system with few procedural errors or adverse outcomes.