In 2010 the Belgian government introduced a low cost administrative procedure for compensating medical injuries to overcome the major shortcomings of the existing tort system. This paper examines, for the first time, to what extent this reform had an impact on physician specialists’ defensive practices and what are the relevant determinants affecting physicians’ clinical decision making. Based on a survey of 508 physicians, we find evidence of a relatively modest increase in defensive practices among physicians in various specialties. In general, 14% of the respondents, who were aware of the reform, reported to have increased their overall defensive behaviour, while respectively 18 and 13% altered their assurance and avoidance behaviour. Commonly used physician characteristics, such as claims experience and gender, have a similar impact on defensive medicine as documented in existing literature. Furthermore, the determinant physician’s access to an incident reporting system is found to have a significant impact on most of the defensive medicine measures. Health care institutions may therefore play an important role in controlling and reducing physicians’ defensive practices.