BACKGROUND Surveys have demonstrated that primary care physicians are aware of cancer screening and prevention guidelines. However, health primary care providers do not recommend these services for many patients. This introductory discussion describes a new area of clinical study: practice barriers. METHODS Literature review and the author's synthesis are used to identify major types of obstacles impeding broad implementation of cancer screening and prevention. RESULTS Practitioners and patients face three types of obstacles: provider-specific obstacles; patient-specific obstacles; and health care delivery system obstacles. Provider-specific obstacles include lack of time, distraction by other health issues, lack of expertise, lack of positive feedback, and disagreement with recommendations. Barriers that chiefly affect screening for the major cancer sites (breast, colon, and cervix) and obstacles affecting preventive counseling also are discussed. Several techniques to help providers overcome obstacles have proven successful in increasing preventive activities. CONCLUSIONS Efforts to increase cancer screening and prevention must focus on helping providers identify and overcome barriers through acquisition of needed skills, refinement of office time management, implementation of effective reminder systems, and development of appropriate, innovative feedback and reward mechanisms.