AIM: To describe factors associated with an increased chance of survival among patients suffering from an out-of-hospital cardiac arrest in Sweden. PATIENTS AND METHODS: All patients suffering from an out-of-hospital cardiac arrest, which were not crew witnessed, in Sweden and in whom cardiopulmonary resuscitation (CPR) was attempted and who were registered in the Swedish Cardiac Arrest Registry. This registry covers about 85% of the Swedish population and has been running since 1990. RESULTS: In all, 33,453 patients, 71% of whom had a cardiac etiology, were included in the survey. The following were independent predictors for an increased chance of survival in order of magnitude: (1) patients found in ventricular fibrillation (odds ratio [OR] 5.3, 95% confidence limits [CL] 4.2-6.8), (2) the interval between call for and arrival of the ambulance less than or equal to the median (OR 3.6, 95% CL 2.9-4.6), (3) cardiac arrest occurred outside the home (OR 2.2, 95% CL 1.9-2.7), (4) cardiac arrest was witnessed (OR 2.0, 95% CL 1.6-2.7), (5) bystanders performing CPR before the arrival of the ambulance (OR 2.0, 95% CL 1.7-2.4), and (6) age less than or equal to the median (OR 1.6, 95% CL 1.4-2.0). When none of these factors were present, survival to 1 m was 0.4%; when all factors were present, survival was 23.8%. CONCLUSION: Among patients suffering from an out-of-hospital cardiac arrest, which were not crew witnessed, in Sweden and in whom CPR was attempted, 6 factors for an increased chance of survival could be defined. These include (1) initial rhythm, (2) delay to arrival of the rescue team, (3) place of arrest, (4) witnessed status, (5) bystander CPR, and (6) age.