OBJECTIVE--To describe the proportion of patients who were discharged from hospital after witnessed cardiac arrest outside hospital in relation to whether a bystander initiated cardiopulmonary resuscitation. PATIENTS--All patients with witnessed cardiac arrest outside hospital before arrival of the ambulance and in whom cardiopulmonary resuscitation was attempted by the emergency medical service in Gothenburg during 1980-92. RESULTS--Cardiopulmonary resuscitation was initiated by a bystander in 18% (303) of 1,660 cases. In this group 69% had ventricular fibrillation at first recording compared with 51% in the remaining patients (P