We analysed research ethics committee (REC) letters. We found that RECs frequently identify process errors in applications from researchers that are not deemed “favourable” at first review. Errors include procedural violations (identified in 74% of all applications), missing information (68%), slip-ups (44%) and discrepancies (25%). Important questions arise about why the level of error identified by RECs is so high, and about how errors of different types should be handled.