Data about tobacco and alcohol consumption are essential in many types of studies. These data can be obtained by directly questioning patients or by using the information collected from physicians. Agreement between these two sources varies according to the characteristics of patients but probably also those of physicians. The purpose of this study was to analyze the characteristics of general practitioners (GPs) associated with agreement between them and their patients about the patients' consumption of alcohol and tobacco. Data came from an observational survey among GPs who were internship supervisors in the Paris metropolitan area. Fifty-two volunteer GPs completed a self-administered questionnaire about the organization of their practice and their training. For each GP, a random sample of 70 patients, aged 40 to 74 years, answered questions about their personal tobacco and alcohol consumption. GPs simultaneously answered similar questions about each patient. We used a mixed logistic model to assess the association between physicians' characteristics and agreement for patients' smoking status and alcohol consumption. Data were collected from both patient and physician for 2599 patients. The agreement between patients and their physicians was 60.4% for smoking status and 48.7% for alcohol consumption. Physicians with continuing medical education in management of smokers and those reporting specific skill in managing hypertension had the best agreement for smoking. Physicians who taught courses at the university medical school and those reporting specific skill in managing alcoholism had the best agreement for alcohol consumption. Agreement increases with physicians' training and skills in management of patients with tobacco and alcohol problems. It supports the importance of professional training for improving the quality of epidemiologic data in general practice. Researchers who use GPs as a source of information about patients' tobacco and alcohol consumption must assess the physicians' characteristics.