Registration audit of clinical trials given a favourable opinion by UK research ethics committees.

Despite researchers and sponsors being reminded that registration of clinical trials is a condition of the research ethics committee (REC) favourable opinion, one-fifth of clinical trials either had not been registered, or their registration could not easily be found, 14 to 20 months after receiving the favourable opinion letter. The methodology trialled here proved effective, and although there are positive indications of a culture change towards greater registration, our results show that more still needs to be done to increase trial registration.