The authors conducted a study of primary care physicians in the province of Quebec to ascertain their patterns of preventive practice with respect to cancer in four anatomic sites: breast, cervix, colon-rectum, and lung. They further explored the data set to elicit the determinants of the patterns of preventive practice. Scales were constructed encompassing practice behaviors for each type of cancer, continuing education intensity, knowledge, and belief. The content of these scales was delineated through factor analysis and their reliability assessed using Cronbach's alpha. Other variables were also considered in the conceptual model. Bivariate analysis and multivariate techniques were used. The models tested contained many significant interaction terms. A limited number of the first-order interactions was explored for each of the dependent variables. Different patterns emerged for each cancer type. Mode of reimbursement, continuing education, gender of physician, provider-related barriers to prevention, and knowledge were found to be the major predictors of prevention scores for the cancers studied, but their relative importance varied according to each cancer. The importance of better understanding the determinants of physician behaviors is emphasized and the existence of several possible explanatory models suggested.