BACKGROUND: Little is known about the immediate outcomes of the Mobile Emergency Medical Services (SAMU) in Brazil. OBJECTIVE: To evaluate clinical predictors of survival of patients in cardiorespiratory arrest (CRA) in the nonhospital environment treated by the SAMU in the city of Porto Alegre. METHODS: The present study has a prospective and observational design. The evaluated outcomes were 30-day survival and hospital discharge, in addition to the Cerebral Performance Category (CPC) score I-II. RESULTS: From January to October 2008, a total of 593 patients in nontraumatic CRA were treated and 260 cardiopulmonary resuscitation (CPR) attempts were made. There was an initial successful outcome in 52 (20.0%) cases, with 16 patients (6.0%) alive on the 30th day and 10 being discharged from the hospital (3.9%), of which 6 (2.3%) presented CPC I-II score. The CPR at home was inversely associated with 30-day survival (p = 0.001) and hospital discharge survival (p = 0.02). An initial “shockable” rhythm (p = 0.008) was associated with 30-day survival. The response-time and collapse-time intervals until CPR start were significantly shorter in 30-day survivors. At multivariate analysis, independent 30-day mortality predictors were an initial shockable rhythm (odds ratio [OR] = 0.28 and 95% confidence interval [95%CI] = 0.10 – 0.81; p = 0.02) and CPR at home (OR = 3.0 and 95CI% = 1.04 – 8.7; p = 0.04). CONCLUSION: The pre-hospital care of CRA in the city of Porto Alegre has limited results; however, they are comparable to the results from other international locations. It is necessary to reinforce each link of the survival chain to improve pre-hospital care, aiming at improving clinically relevant outcomes.