The physician-patient relationship has always been of interest to family physicians. This paper describes a component of the physician-patient relationship in family medicine, originally identified by Michael Balint, that operates parallel to and in conjunction with the biopsychosocial model: the family physician's personal knowledge of patients. The physician's personal knowledge of patients is a personal information network about particular patients who the physician has cared for over a series of encounters spanning several years. It is a detailed portrait painted with layers of fact, intuition, and experience and is comprised of a mix of clinical art, science, psychodynamics, and ethics. It may be factual, intuitive, or contain components of countertransference; it differs from Kleinman's concept of explanatory model in that it belongs to the physician and is employed for the benefit of the patient. It is neither paternalistic nor static. The family physician's personal knowledge for his or her patients is a seldom-measured but common component of the process of making medical, ethical, and pragmatic patient care decisions. The presence of this knowledge and its skillful use may mark one difference between novice and seasoned clinicians. Qualitative methods are most appropriate for exploring the breadth and depth of this concept, while quantitative methods are useful for studying its implications for clinical decision making and quality of care in family practice.