Hundreds of runners from across Yorkshire are at Newby Hall, near Ripon to take part in the Yorkshire 10k.
It is open to everyone over 16 and there is also a 2 run.
Runners are raising money for the Cystic Fibrosis Trust and all money raised will go to funding medical research.
Between mid-October and December 2011, samples from 15,000 babies across South Yorkshire, Lincolnshire and the East Midlands were put through the faulty cystic fibrosis testing machine in Sheffield. All those families have now been contacted and youngsters given the all clear.
The NHS has admitted there was a fault with a machine used to test newborn babies in South Yorkshire and Lincolnshire for cystic fibrosis. Parents of children affected have been sent letters informing them of the problem. All those youngsters have now been checked and given the all clear.
Trials are due to begin on a treatment for cystic fibrosis which replaces a faulty gene and stops mucus forming in the lungs.
Toni Hannon is from Ripon and her son Evan has the condition. When he's ill he coughs, has night sweats and panic attacks, vomits and is always tired.
She's raised money in the past for research into the illness.