Purpose: The Basque Autonomous Community (BAC) is a 2.2 million community covering 7200km2, with 250 municipalities and three cities (>150,000 inhabitants) accounting for 35.4% of the population. Out-of-hospital cardiac arrest (OHCA) is attended by a two-tiered EMS system. Large differences in OHCA survival exist between the arrests occurring in main cities and in the rest of locations. The objective of this study was to compare factors affecting survival in patients with OHCA in the BAC between arrests occurring in cities and the rest of municipalities. Materials and methods: Data were collected in Utstein-style between June 2013 and December 2014. For the analysis arrests with known initial rhythm that were not witnessed by EMS were included. Variables were compared between arrests occurring in cities and the rest of municipalities. Stepwise logistic regression wasused to select independentdichotomouspredictors for survival with favorable neurological outcome (CPC1–2) for all arrests, and to compute adjusted odds-ratios (aOR) with 95% confidence intervals (CI). Arrest occurring in a city was included in the model.