Thirty-eight races in the north-west of England are being investigated by the Association of UK Course Measurers for being too short.
It follows three years of Greater Manchester Marathon times being declared invalid in April after the course was found to be short by 380m.
Courses are measured using a bicycle fitted with a counter to calculate distance by the turning of the wheels.
However, the course used to calibrate the bicycle wheel was short by 0.5%.
So far, five of the affected 39 courses - including the Greater Manchester Marathon - have been re-measured and all have been found to be short. They are:
- Greater Manchester Marathon
- Buxton Half Marathon
- Buxworth 5 (five-mile)
- Trafford 10K
- Christleton 5K
Volunteers are re-measuring a further three courses believed to have used the same device to calculate their race routes. They are:
- Oldham Half Marathon
- Littleborough 5k
- High Legh 10k
UK Athletics has said it will not recognise times from the three Greater Manchester Marathon races that were measured wrongly.
However, the error was corrected in time for this year's event, which was held on 10 April.