fa عمومى General پژوهشي Research <p style="text-align: justify;"><strong>Background:</strong> Identification of the effective factors in reducing response time in prehospital emergency medical service (EMS) can assist in improving its services. This study aimed at reviewing the effect of applying global positioning system (GPS) on response time of Tehran EMS ambulances.<br> <strong>Materials and Methods:</strong> Of 132 Tehran EMS stations, 24 ones were randomly selected, and relevant data, including the response time of all missions in 2009 (without GPS) and in 2011 (with GPS) as well as number of daily calls to &nbsp;each dispatch center were extracted. The average number of daily calls in the call centers were categorized into 3 groups as follows: I) &le;10 calls, II) 10 to 15 calls, and III) >15 calls. The statistical analysis of the obtained data was carried out by paired t test.&nbsp;<br> <strong>Results:</strong> The findings revealed that the average response times in 2009 for the 3 groups (I, II, and III) were 10.11, 11.25, and 10.92 minutes, respectively. These times recorded for groups (I, II, and III) in 2011 were 9.86, 10.71, and 11.58 minutes, respectively, which were significantly less than the response times recorded in 2009 (P<0.001).<br> <strong>Conclusion:</strong> This research has demonstrated that the application of GPS in the ambulances may be essential in the reduction of response time, especially in emergency stations with more average mission numbers</p> Prehospital, Emergency medical service, Global positioning system, Ambulance, Response time, Tehran 125 128 http://hdq.uswr.ac.ir/browse.php?a_code=A-10-25-3&slc_lang=fa&sid=1 Vahid Delshad No Department of Health in Emergency and Disaster Research Center, University of Social Welfare and Rehabilitation Sciences, Tehran, Iran. Hashem Shemshadi No Department of Clinical Sciences, University of Social Welfare and Rehabilitation Sciences, Tehran, Iran. Mohammad Javad Moradian No Department of Disaster Public Health, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran. Shokoufeh Ahmadi No Department of Health in Emergency and Disaster Research Center, University of Social Welfare and Rehabilitation Sciences, Tehran, Iran. Lila Malkyan No Department of Nursing, Faculty of Nursing and Midwifery, Bam University of Medical Sciences, Bam, Iran Samaneh Sabzalizadeh alizade.samaneh@gmail.com Yes Health Technology Office, Vice Chancellor for Research & Technology, Univereity of Social Welfare and Rehabilitation Sciences, Tehran, Iran.