BACKGROUND: Clinical practice guidelines, such as those of the Canadian Task Force on Preventive Health Care, although based on sound evidence, may conflict with the perceived needs and expectations of patients and physicians. This may jeopardize the implementation of such guidelines. This study was undertaken to explore patients' and family physicians' acceptance of the task force's recommendations and the values and criteria upon which the opinions of these 2 groups are based. METHODS: Focus groups were used to collect study data. In total, 35 physicians (in 7 groups) and 75 patient representatives (in 9 groups) participated in the focus groups. An inductive approach was used to develop coding grids and to generate themes from the transcripts of the interviews. RESULTS: Physicians expressed resistance to discontinuing the annual check-up, which they viewed as an organizational strategy to counteract the many barriers to preventive care that they encounter. They reported difficulties in explaining to their patients the recommendations of the Canadian Task Force on Preventive Health Care, which they found complex and inconsistent with popular wisdom. Both patients and physicians attributed high value to the detection of insidious diseases, even in the absence of proof of the effectiveness of such activity. INTERPRETATION: The patients and family physicians who participated in this study shared many opinions on the value of preventive activities that depart from the values used by "prevention experts" such as the Canadian Task Force on Preventive Health Care in establishing their recommendations. A better understanding of the values of patients and physicians would help guideline developers to create better targeted communication strategies to take these discrepancies into account.