['To compare the outcomes of out-of hospital cardiac arrest (OHCA) victims treated with monophasic truncated exponential (MTE) versus biphasic truncated exponential (BTE) defibrillation in an urban EMS system.', 'We conducted a retrospective review of electronic prehospital and hospital records for victims of OHCA between August 2000 and July 2004, including two years before and after implementation of biphasic defibrillators by the Fresno County EMS agency. Main outcome measures included: return of spontaneous circulation (ROSC), number of defibrillations required for ROSC, survival to hospital discharge, and discharge to home versus an extended care facility.', 'There were 485 cases of cardiac arrest included. Baseline characteristics between the monophasic and biphasic groups were similar. ROSC was achieved in 77 (30.6%, 95% CI 25.2-36.5%) of 252 patients in the monophasic group, and in 70 (30.0% 95% CI 24.5-36.2%) of 233 in the biphasic group (p= .92). Survival to hospital discharge was 12.3% (95% CI 8.8-17%) for monophasic and 10.3% (95% CI 7.0-14.9%) for biphasic (p= .57). Discharge to home was accomplished in 20 (7.9%, 95% CI 5.1-12.0%) of the monophasic, and in 15 (6.4%, 95% CI 3.9-10.4%) of the biphasic group (p= .60). More defibrillations were required to achieve ROSC (3.5 vs. 2.6, p= .015) in the monophasic group.'] Does biphasic defibrillation improve outcomes compared to monophasic defibrillation in out-of-hospital cardiac arrest?