The Suwa Onbashira Festival is held every six years and draws approximately one million spectators from across Japan. Men ride the Onbashira pillars (logs) down steep slopes.At each festival, several people are crushed under the heavy log. During the 2004 festival, for the first time, a medical care system that coordinated a medical team, an emergency medical service, related agencies, and local hospitals was constructed.

The aims of this study were to characterize the spectrum of injuries and illness and to evaluate the medical care system of this festival.

The festival was held 02 April–10 May 2004. The medical records of all of the patients who presented to an on-site medical tent or who were treated at the scene and transported to hospitals over a 12-day period were reviewed.The following items were evaluated: (1) the emergency medical system at the festival; (2) the environmental circumstances; and (3) patient data.

All medical usage rates are reported as patients per 10,000 attendees (PPTT). A total 1.8 million spectators attended the festival during the 12-day study period; a total of 237 patients presented to the medical tent (1.32 PPTT), and 63 (27%) were transferred to hospitals (0.35 PPTT). Of the total, 135 (57%) suffered from trauma—two were severely injured with pelvic and cervical spine fractures; and 102 (43%) had medical problems including heat-related illness.

Comprehensive medical care is essential for similar mass gatherings. The appropriate triage of patients can lead to efficient medical coverage.