The Cardiff Half Marathon is a 25,000 sell-out for the first time, organisers have confirmed.
Wales' largest mass participation race takes place around the capital's streets on Sunday, 1 October.
A spokesman for organiser Run4Wales said the number of entrants breaks last year's record of 22,000 runners.
Since its inception in 2003, it has become the UK's second largest event of its kind and last year participants raised £2.5m for charity.
This year's route starts outside Cardiff Castle and will take runners past Cardiff City Stadium to Penarth, before they cross to Cardiff Bay and complete a loop of Roath Park Lake.