We used the data of 5,712 patients at least 18 years of age, enlisted in 2007-2009 in 5 GP practices in one primary healthcare centre in Amsterdam, the Netherlands. These practices participated in the GP-based continuous morbidity registration network of the Department of General Practice at the Academic Medical Center of the University of Amsterdam. In this GP network, electronic medical record data are extracted for research purposes. We used only face-to-face consultations with the GP (consultations in the surgery and house-calls). Patients under the age of 18 years were excluded, because their consultations often involved the parents as well as the patient. Because only a proportional threshold definition selects the exceptional users within each sex and age group and allows more meaningful comparisons between practices, periods and countries, we defined FAs as the age and sex-adjusted (18-30 years; 31-45 years; 46-60 years; 61 years+) top 10 centile attenders within a time frame of one year (1-year frequent attenders).3;8 FAs were determined for each of the years 2007, 2008 and 2009. One-year frequent attenders (1yFAs) attended frequently in one of those years. We defined 1-, 2-, and 3-year frequent attenders (1-, 2- and 3yFAs) as those patients who were frequent attender in one, two or three of those years, respectively. All other enlisted patients were non-FAs.