The aim of the present study was to examine the relations between continuity of care and the general practitioners' accumulated knowledge about their patients. A further objective was to evaluate the link between continuity of care and the doctors' sense of medical responsibility towards the patients. Emphasis was placed on the chronological, or longitudinal component of continuity of care. In a cross-sectional record study a representative sample of 133 Norwegian general practitioners each registered 30 consecutive consultations. Two aspects of longitudinal care were recorded: the duration of the patient-doctor relationship, measured as time from the first visit to the present, and the density, measured as the number of consultations (office or home visits) within the last 12 months. The physicians subjectively evaluated their accumulated knowledge about the patient's medical history, personality, and social network, on multinomic scales. Their sense of medical responsibility was indicated as one of three alternatives. Of 3990 possible recordings, 3918 (98%) were evaluated. In about one-third of all encounters the doctors reported extensive knowledge about their patients. It took at least one, and often 5 years, or at least 4-5 visits last year, to create such an extensive knowledge base. The physician's sense of responsibility increased more rapidly, and to a higher degree with the density of visits, than with duration of the relationship. The findings indicate firm links between longitudinal care and accumulated knowledge, and between longitudinal care and the doctors' sense of responsibility towards their patients.