INTRODUCTION:Substance use disorders (SUD) in physicians often remain concealed for a long time. Peer monitoring and open discussions with colleagues are essential for identifying SUD. However, physicians often feel uncomfortable discussing substance use with a colleague. We explored physicians' attitudes and norms about substance use (disorders) and their (intended) approach upon a presumption of substance use in a colleague. MATERIALS AND METHODS:An online cross-sectional survey concerning "Addiction in physicians" was administered by the Royal Dutch Medical Association physician panel. Overall, 1685 physicians (47%) responded. Data were analyzed by logistic regression to explore factors associated with taking action upon a substance use presumption. RESULTS:Most physicians agreed that SUD can happen to anyone (67%), is not a sign of weakness (78%) and that it is a disease that can be treated (83%). Substance use in a working context was perceived as unacceptable (alcohol at work: 99%, alcohol during a standby duty: 91%, alcohol in the eight hours before work: 77%, and illicit drugs in the eight hours before work: 97%). Almost all respondents (97%) intend to act upon a substance use presumption in a colleague. Of the 29% who ever had this presumption, 65% took actual action. Actual action was associated with male gender and older age (OR = 1.81; 95% CI = 1.20-2.74 and OR = 1.03; 95% CI = 1.01-1.05, respectively). CONCLUSIONS:About one-third of physicians reported experience with a presumption of substance use in a colleague. Whilst most physicians intend to take action upon such a presumption, two-thirds actually do act upon a presumption. To bridge this intention-behavior gap continued medical education on signs and symptoms of SUD and instructions on how to enter a supportive dialogue with a colleague about personal issues, may enhance physicians' knowledge, confidence, and ethical responsibility to act upon a presumption of substance use or other concerns in a colleague.