Background Emergency Medical Services (EMS) provide effective and coordinated care to people in need due to a medical emergency, in both hospital and pre-hospital settings. A proper and opportune care is associated with less mortality and disability. In Mexico, no information is available about the association of the opportunity of EMS response and its results in terms of health outcomes.

Methods Information from all patients with Road Traffic Injuries (RTI) was collected through an epidemiological surveillance system between 2012–2014 in two general hospitals located in two Mexican cities. A multinomial logistic regression model explored the association between health consequences (0 = received care in hospital emergency rooms <24 hrs, 1 = was hospitalised, 2 = was permanently disabled and 3 = died) with opportunity of EMS (quantified in terms of time since the injury occurred until they received EMS care) adjusting by different covariables of interest: sex, age, Injury Severity Score, received pre-hospital care (PHC), type of road user, use of safety devices, alcohol consumption 6 hrs previous to the event.

Results 2,575 people injured received EMS in both hospitals. Of them, 64% required care in hospital <24 hrs, 27% were hospitalised, 6% suffered permanent disability and 3% died. About 47% received PHC in León and 38% in Guadalajara. Time to access EMS was 32 min in Guadalajara and 38 in León; those who received PHC had lower times compared to those who did not in both cities. Opportunity of EMS was only associated to being hospitalised: the lower the time, the lower the likelihood of being hospitalised adjusting by covaraibles of interest. According to our data, opportunity of EMS was not statistically associated to disability and death.

Conclusions Authorities should promote strategies to comprehensively evaluate and improve quality as well as opportunity of EMS care in both cities.