On Sunday 11 June 2006, 8000 people undertook a “fun run” in Hyde Park, the BUPA Capital 10K. During the course of the afternoon, St Mary’s Hospital emergency department received four, and another local hospital received three, collapsed adult runners.

All collapsed at 7–10 km, were confused, and showed signs of severe heat stroke (with core temperatures of 40–41°C). Three patients required intubation, and three required sedation and high dependency unit care. One patient was admitted to the intensive care unit for 72 hours. Happily all survived, but there are some important lessons to be learnt for future similar events.

No official temperatures were recorded at …