AimThis study aimed to reveal the characteristics and outcomes of patients with out-of-hospital cardiac arrests (OHCAs) occurring in the toilet. These traits provide useful clues for the prevention of OHCAs and the improvement of prehospital care for these patients.MethodsOut-of-hospital cardiac arrest data were obtained from the population-based, Utstein-style registry in Osaka City, Japan, between 2009 and 2015. This study identified patients with OHCAs that occurred inside the toilet. The primary end-point was 1-month survival with favorable neurological outcome after OHCA.ResultsDuring the 7-year study period, a total of 18,458 OHCAs were identified. Of these cases, 849 (4.6%) occurred inside the toilet. Among them, the analysis included 733 patients. The distribution depicting monthly OHCA occurrences showed that OHCAs tended to occur in cold months (28.1% [206/733] from October to December and 30.0% [220/733] from January to March). Most OHCAs occurring inside the toilet were of cardiac origin (91.5% [671/733]), and 36.2% (265/733) were witnessed by bystanders. The proportion of patients with ventricular fibrillation was 5.2% (38/733) and those receiving shocks by public-access automated external defibrillators was 0.4% (3/733). The proportion of patients with 1-month survival with favorable neurological outcome was 1.9% (14/733).ConclusionsOut-of-hospital cardiac arrests occurring inside the toilet accounted for 4.6% of all OHCAs and were frequently observed during cold months, and their outcome was poor. Establishment of preventive measures against OHCAs occurring in the toilet as well as earlier recognition of OHCAs are needed.