AIM: To describe various factors at resuscitation and outcome among patients suffering from out-of-hospital cardiac arrest in relation to age. PATIENTS: All patients included in the Swedish Cardiac Arrest Registry during the period 1990-1999. The registry covers about 60% of all ambulance organisations in Sweden. METHODS: All patients reached by the ambulance crew and in whom resuscitative efforts were attempted. Crew witnessed cases were excluded. Only patients aged over 18 years were included. Patients were divided into three age groups: less than 65 years (n=7810), 65-75 years (n=7261) and over 75 years (n=8390). RESULTS: The proportion of cases with a cardiac aetiology increased with increasing age (P<0.0001). The proportion of witnessed cases increased with increasing age among those with a non-cardiac aetiology (P<0.0001) and decreased with increasing age among cases with a cardiac aetiology (P=0.02). The proportion of patients exposed to bystander CPR decreased with increasing age (P<0.0001). The proportion of patients found in ventricular fibrillation (VF) decreased with increasing age among patients with a cardiac aetiology (P<0.0001) but was not related to age in those with a non-cardiac aetiology. The proportion of patients being alive after 1 month in the three age groups (youngest first) were: 4.5, 3.2 and 2.5% (P<0.0001). The corresponding figures for patients with a cardiac aetiology found in VF were: 10.7, 7.6 and 6.6% (P<0.0001). After multiple regression analysis controlling for other factors increasing age was still associated with decreased survival to 1 month (odds ratio 0.85; 95% confidence limits 0.80-0.91). CONCLUSION: Among patients suffering from out-of-hospital cardiac arrest various factors at resuscitation, including initial rhythm, aetiology and bystander CPR, are strongly related to age. The chance of survival diminishes with increasing age. When correcting for the dissimilarities in terms of factors at resuscitation, age is still significantly associated with survival, being lower among the elderly.