A prospective observational study of 4,653 consecutive cases of out-of-hospital cardiac arrest (OOHCA) occurring in New York City from April 1, 2002, to March 31, 2003, was used to assess racial/ethnic differences in the incidence of OOHCA and 30-day survival after hospital discharge among OOHCA patients. The age-adjusted incidence of OOHCA per 10,000 adults was higher among Blacks than among persons in other racial/ethnic groups, and age-adjusted survival from OOHCA was higher among Whites compared with other groups. In analyses restricted to 3,891 patients for whom complete data on all variables were available, the age-adjusted relative odds of survival from OOHCA among Blacks were 0.4 (95% confidence interval: 0.2, 0.7) as compared with Whites. A full multivariable model accounting for demographic factors, prior functional status, initial cardiac rhythm, and characteristics of the OOHCA event explained approximately 41 percent of the lower age-adjusted survival among Blacks. The lower prevalence of ventricular fibrillation as the initial cardiac rhythm among Blacks relative to Whites was the primary contributor. A combination of factors probably accounts for racial/ethnic disparities in OOHCA survival. Previously hypothesized factors such as delays in emergency medical service response or differences in the likelihood of receipt of cardiopulmonary resuscitation did not appear to be substantial contributors to these racial/ethnic disparities.