ConclusionIn this analysis of prospective data collected by the ROC in multiple large geographically separate sites, the provision of ALS care, when compared with BLS-only care, was associated with increased ROSC and with survival to hospital discharge except when ALS care was provided late in the resuscitation. ALS care was not associated with improved functional status. A better understanding of the precise mechanisms by which ALS care improves ROSC provides a promising strategy to improve outcomes for OHCA victims