Continuity of care is claimed to be an important and integral part of general practice. A main result of continuity is the doctor's accumulated knowledge about his or her patients. The objective of the present study was to evaluate the modifying effects of this knowledge on the decision-making process that takes place in consultations, as experienced by practitioners. A representative sample of 133 Norwegian general practitioners evaluated a total of 3,918 of their own consultations. The main independent variable was the doctor's own subjectively evaluated knowledge about the patient's medical history, while the major outcome measures included the perceived influence of accumulated knowledge on the consultation process in general, and on the diagnostic and management decisions in particular. In two-thirds of all consultations, or in three out of four in which the doctor had previous knowledge about the patient, this knowledge was considered to be clinically useful. In more than one-third of all consultations with previously unknown patients, this lack of information was felt to be a hindrance. Among patients with new medical problems and when the doctor had prior knowledge about the patient, this knowledge was felt to have significantly more therapeutic than diagnostic impact. Accumulated knowledge was generally felt to be of most help in consultations due to psycho-social problems, and was of special diagnostic value in patients presenting new, unspecific problems such as fatigue, fever, and generalized pain. This study indicates that accumulated knowledge about the patient is felt by the general practitioners to play an important and integral part in their clinical decision-making process.