Background: In out-of-hospital cardiac arrest (OHCA), 10-50% of patients have return of spontaneous circulation (ROSC) before hospital arrival. It is important to investigate the relation between time-to-ROSC and survival to determine the optimal timing of transport to the hospital in patients without ROSC. Methods: We analyzed data of OHCA patients with a presumed cardiac cause (excluding traumatic and other obvious non-cardiac causes) and ROSC before hospital arrival from the Amsterdam Resuscitation Study (ARREST) database. ROSC included those patients whose ROSC was persistent or transient before or during transport, lasting !1min. Of these data, we analyzed the association between the time of emergency medical services (EMS) arrival until ROSC (time-to-ROSC) and 30-day survival. Results: Of 3632 OHCA patients with attempted resuscitation, 810 patients with prehospital ROSC were included. Of these, 332 (41%) survived 30 days. Survivors had a significant shorter time-to-ROSC compared to non-survivors of median 5 min (IQR 2,10) vs. median 12 min (IQR 9,17) (p < 0.001). Of the survivors, 90% achieved ROSC within 15 min compared to 22 min of non-survivors. In a multivariable model adjusted for known system determinants time-to-ROSC per minute was significantly associated with 30-day survival (OR 0.89; 95%CI 0.86-0.91). A ROC curve showed 8 min as the time-to-ROSC with the best test performance (sensitivity of 0.72 and specificity of 0.77). Conclusion: In OHCA patients with prehospital ROSC survival significantly decreases with increasing time-to-ROSC. Of all patients, 90% of survivors had achieved ROSC within the first 15 min of EMS resuscitation. The optimal time for the decision to transport is between 8 and 15 min after EMS arrival.