BACKGROUND In-depth analysis of emergency medical services (EMSs) performances in out-of-hospital cardiac arrest (OHCA) promotes quality improvement. AIMS The purpose of this study was to identify the improvable factors of the EMS response to OHCA through the description and analysis of OHCA incidence, characteristics, management and outcome. METHODS This was a retrospective cohort study on all OHCA patients treated by the EMSs of the district of Trieste, Italy (236,556 inhabitants) in 2011. RESULTS A total of 678 OHCAs occurred and 142 (20.1%) underwent cardiopulmonary resuscitation (CPR), with a respective incidence of 287/100,000/year and 60/100,000/year. The incidence of shockable rhythms in the CPR group was 13/100,000. OHCAs occurred mainly during daytime, though the proportion of patients receiving CPR was significantly higher by night-time (p=0.01). Thirty-four CPR patients (23.9%) restored spontaneous circulation on scene; 12 (8.5%) survived to hospital discharge (11 with good neurological recovery). Survival was not correlated with age, while was significantly higher for patients with shockable rhythms (32.3%; p<0.001). Mean response time was 8 min. Direct intervention of physician-staffed units did not improve the outcome when compared with two-tiered activation. Patients immediately identified as OHCA by dispatch nurses and those undergoing therapeutic hypothermia showed a non-significant trend towards improved survival (p=0.09 and 0.07, respectively). CONCLUSIONS OHCA identification by dispatch nurses and reduction of response time were the factors most susceptible to improvement.