Introduction - In 2003, the surveillance system for notifiable diseases underwent significant changes, with measures taken to strengthen the anonymity of individuals in order to facilitate the launch of new notifiable disease programs, particularly those involving biologists. Methods - In 2005, an assessment of potential reporters’ knowledge and attitudes toward MDOs, as well as an evaluation of reporting practices, was conducted via telephone interviews. Two representative samples of 400 physicians from eight medical specialties and 400 biologists were randomly selected using a stratified random sampling method. Results - Among laboratory scientists, 78% were familiar with at least two of 26 ADRs, and 42% had reported at least one since 2003. Among physicians, 77% could name two ADRs, and 23% had submitted at least one report. Among laboratory scientists and physicians who were familiar with two ADRs but had never reported one, half had diagnosed at least one. Barriers to reporting are primarily linked to a lack of understanding of their role and the process. Among those who report, the system is generally well accepted. However, one-quarter of biologists and 38% of reporting physicians believe the procedure is too administrative and time-consuming. Better information, targeted feedback, and the digitization of the process are among the desired improvements. Conclusion - DO is well accepted by those who use it. The main barriers to reporting remain a lack of understanding of the system and the perception that it is an administrative task for others. DO remains an administrative and complex process for some reporters. Efforts to raise awareness among stakeholders and improvements to the system are necessary. (R.A.)