Although regional variation in outcome after adult out-of-hospital cardiac arrest (OHCA) is known, no clinical studies have assessed this in pediatric OHCA. This nationwide, prospective, population-based observation of the whole of Japan included consecutive OHCA patients with resuscitation attempt from January 2005 through December 2009. Primary outcome was 1-month survival with neurologically favorable outcome. Japan was divided into the following 7 regions as the largest administrative units: Hokkaido-Tohoku, Kanto, Tokai-Hokuriku, Kinki, Chugoku, Shikoku, and Kyushu-Okinawa. The outcome of pediatric OHCA was then compared between the regions. Multiple logistic regression analysis was used to adjust for other factors that were considered to influence the relationship between region and outcome. A total of 8,240 pediatric OHCA patients were registered during the study period. One-month survival with neurologically favorable outcome significantly differed by region: 2.5% (24/967) in Hokkaido-Tohoku (adjusted odds ratio [AOR], 1.65; 95% confidence interval [CI]: 0.94-2.90), 2.9% (47/1614) in Tokai-Hokuriku (AOR, 2.06; 95% CI: 1.28-3.31), 2.1% (26/1239) in Kinki (AOR, 1.45; 95% CI: 0.84-2.51), 3.4% (16/465) in Chugoku (AOR, 3.11; 95% CI: 1.62-6.00), 1.5% (4/259) in Shikoku (AOR, 0.79; 95% CI: 0.26-2.43), and 2.8% (27/974) in Kyushu-Okinawa (AOR, 2.15; 95% CI: 1.24-3.74) referred to Kanto (1.4%, 37/2722). According to Japanese nationwide OHCA registry data there are significant regional variations in the outcome of pediatric OHCA.