A mandatory reporting system (MRS) was set up in France in December 1990 to detect animals showing clinical signs of bovine spongiform encephalopathy (BSE). Since June 2000, four active surveillance programmes dedicated to fallen stock and slaughtered cattle have been implemented to reinforce the MRS. The clinical status of the cases detected through these programmes was investigated to understand why the MRS had failed to detect them. Up to September 1, 2002, 181 cases had been analysed (126 fallen stock and 55 slaughtered cattle). Almost all the fallen stock cases were animals which had been showing clinical signs, and two thirds of them had shown signs which should have led to a suspicion of BSE. No clinical signs had been reported for two thirds of the slaughtered cattle cases and 10 (8 per cent) of the fallen stock cases.