The Prime Minister joined competitors on a mile-long route in the Cotswold village of Chadlington.
Face smeared with mud, Mr Cameron crawled under a bridge and stumbled through the water before being congratulated by wife Samantha and receiving a medal and pint of ale.
He wore knee guards to prevent a repeat of the cuts he received during the same event two years ago.
The Great Brook Run has been taking place since 2006, with the slogan ‘Run. Get wet. Have a pint’.
It starts and ends at the Tite Inn in Chadlington, and the website promises that every runner “no matter how crap” gets a medal.
The £5 fee to take part goes to local good causes. Mr Cameron previously participated in 2012 and 2009.