On the average, 10-15% of patients who undergo cardiopulmonary resuscitation (CPR) following a cardiopulmonary arrest in the hospital environment will survive to be discharged. The purpose of this study was to determine objective factors influencing patient outcome after CPR to determine who should be resuscitated and when to end CPR efforts. The records of 266 patients who underwent in-hospital CPR over a 3-year period were retrospectively analyzed with regard to age, gender, co-morbid conditions, setting of arrest, duration of resuscitation, initial pH and PO2 during resuscitation, and outcome of resuscitative efforts. Twenty-four (9%) patients survived to be discharged from hospital. Eighty-seven (33%) patients arrested in the intensive care unit, 77 (29%) on the ward, 91 (34%) in the emergency room, six (2%) in the cardiac catheterization laboratory and five (2%) in the operating room. There was no significant difference in survival based on location of arrest. Factors associated with a poor prognosis included age greater than 60, co-morbid disease (i.e. pneumonia, sepsis, renal failure, heart disease, etc.), an initial PO2 < 50 mmHg and CPR efforts extending beyond 10 min. Based on this data, guidelines regarding initiation and termination of CPR should be instituted in light of poor outcome in patients over 60 years of age with co-morbid conditions, specifically after 10 min of CPR.