The GMC said a 'clerical error' meant that 209 doctors were mistakenly sent letters asking for feedback on their recent fitness-to-practise procedures.
GMC chief executive Niall Dickson said he was 'very sorry for the upset' that this error may have caused. He said he would write personally to all doctors involved to apologise.
The error occurred when the GMC wrote to 2,500 doctors who had undergone fitness-to-practise procedures, which had been closed in 2010, asking for feedback on their experience.
The survey was part of a GMC to drive to improve the way it handles complaints about doctors.
Mr Dickson said: 'Unfortunately as a result of a clerical error 209 doctors who had not been investigated were included in this mailing.
'I am very sorry for the upset that receiving one of these letters may have caused and am writing today to all those doctors involved to apologise.'