Objectives To determine whether there are prehospital differences between blacks and whites experiencing out-of-hospital cardiac arrest and to ascertain which factors are responsible for any such differences.

Methods Cohort study of 3869 adult patients (353 blacks and 3516 whites) in the Illinois Prehospital Database with out-of-hospital cardiac arrest as a primary or secondary indication for emergency medical service (EMS) dispatch between 1 January 1996 and 31 December 2004.

Results Return of spontaneous circulation was lower for black patients (19.8%) than for white patients (26.3%) (unadjusted OR 0.69, 95% CI 0.53 to 0.91). After adjusting for age, sex, prior medical history, prehospital event factors, patient zip code characteristics and EMS agency characteristics, the no difference line was suggestive of a trend, with a CI just transposing 1.00 (adjusted OR 0.71, 95% CI 0.50 to 1.01, p=0.053).

Conclusions Blacks were less likely to experience a return of spontaneous circulation than whites, less likely to receive defibrillation or cardiopulmonary resuscitation from EMS and more likely to receive medications from EMS. Differences in underlying health, care prior to the arrival of EMS, and delays in the notification of EMS personnel may contribute to racial disparities in prehospital survival after out-of-hospital cardiac arrest.