Emergency Medical Service (EMS) can help increase survival rates and reduce possible disability among emergency patients. However, the number of calls for EMS is relatively low in Thailand. This study aimed to inspect the knowledge, perspective, and reasons of calling and not-calling the EMS by patients or their relatives who visited the emergency room in 45 government and private hospitals from December 2015 to February 2016. The hospitals were scattered in 9 provinces with the sample of 2,028 patients, whereby 646 patients had called EMS and 1,368 came by themselves or otherwise. The key reasons for not-calling were: the convenience of personal transportation (76.0%), avoiding waiting time for an ambulance (31.0%), and anxiety on the emergency situation (28.9%). Most misconceptions on the EMS included: (1) Ambulances were used only for casualties from accidents, and (2) Ambulance services were not free. In terms of perspective, most patients or relatives had negative views towards the EMS, especially the idea that they had to help themselves until the condition was severe or medications or relief devices were unavailable. Another view was that the EMS was slower than getting to the hospital on own-self. These perspectives were from non-users more than users. In conclusion, the study indicated that the causes of non-user involved misunderstandings, poor perspectives, and lack of awareness as well as the absence of knowledge on threats related to particular emergency conditions. Hence, regional agencies, the National Institute of Emergency Medicine, and the Ministry of Public Health should discuss the solutions to raise public awareness and to improve the perspective towards the EMS, in order to promote more usage.