BACKGROUND: Outcomes after out-of-hospital cardiac arrests (OHCAs) might be worse during academic meetings because many medical professionals attend them. METHODS: This nationwide population-based observation of all consecutively enrolled Japanese adult OHCA patients with resuscitation attempts from 2005 to 2012. The primary outcome was 1-month survival with a neurologically favorable outcome. Calendar days at three national meetings (Japanese Society of Intensive Care Medicine, Japanese Association for Acute Medicine, and Japanese Circulation Society) were obtained for each year during the study period, because medical professionals who belong to these academic societies play an important role in treating OHCA patients after hospital admission, and we identified two groups: the exposure group included OHCAs that occurred on meeting days, and the control group included OHCAs that occurred on the same days of the week 1 week before and after meetings. Multiple logistic regression analysis was used to adjust for confounding variables. RESULTS: A total of 20 143 OHCAs that occurred during meeting days and 38 860 OHCAs that occurred during non-meeting days were eligible for our analyses. The proportion of patients with favorable neurologic outcomes after whole arrests did not differ during meeting and non-meeting days (1.6% [324/20 143] vs 1.5% [596/38 855]; adjusted odds ratio 1.02; 95% confidence interval, 0.88-1.19). Regarding bystander-witnessed ventricular fibrillation arrests of cardiac origin, the proportion of patients with favorable neurologic outcomes also did not differ between the groups. CONCLUSIONS: In this population, there were no significant differences in outcomes after OHCAs that occurred during national meetings of professional organizations related to OHCA care and those that occurred during non-meeting days.