The benefits of a telemedical support system for prehospital emergency medical services include high-level emergency medical support at the push of a button: delegation of drug administration, diagnostic assistance, initiation of therapeutic measures, or choice of hospital destination. At various European EMS sites telemedical routine systems are shortly before implementation. The aim of this study was to investigate the long-term effects of implementing a tele-EMS system on the structural and procedural quality indicators and therefore performance of an entire EMS system. This retrospective study included all EMS missions in Aachen city between 2015 and 2021. Regarding structural indicators of the EMS system, we investigated the overall number of emergency missions with tele-EMS and onsite EMS physicians. Furthermore, we analyzed the distribution of tracer diagnosis and process quality with respect to the time spans on the scene, time until teleconsultation, duration of teleconsultation, prehospital engagement time, and number of simultaneous teleconsultations. During the 7-year study period, 229,384 EMS missions were completed. From 2015 to 2021, the total number of EMS missions increased by 8.5%. A tele-EMS physician was consulted on 23,172 (10.1%) missions. The proportion of telemedicine missions increased from 8.6% in 2015 to 12.9% in 2021. Teleconsultations for missions with tracer diagnoses decreased during from 43.7% to 30.7%, and the proportion of non-tracer diagnoses increased from 56.3% to 69.3%. The call duration for teleconsultation decreased from 12.07 min in 2015 to 9.42 min in 2021. For every fourth mission, one or more simultaneous teleconsultations were conducted by the tele-EMS physician on duty. The implementation and routine use of a tele-EMS system increased the availability of onsite EMS physicians and enabled immediate onsite support for paramedics. Parallel teleconsultations, reduction in call duration, and increase in ambulatory onsite treatments over the years demonstrate the increasing experience of paramedics and tele-EMS physicians with the system in place. A prehospital tele-EMS system is important for mitigating the current challenges in the prehospital emergency care sector.