BACKGROUND:In extramural setting, general practitioners serve as gatekeepers and therefore control the demand for medical treatment and pharmaceuticals. As a result prescription habits are of major interest. AIM:The aim of the present study is to identify sample characteristics in the prescription behaviour of the general practitioners that allow one to differentiate between the individual and the basic population. METHODS:The prescription behaviour of 4 231 general practitioners was operationalised by means of the two variables "quantity" and "price". Outliers in those categories, that indicate a doctor prescribing too many or too expensive drugs, were identified using Chebyshev's inequality. RESULTS:We found a statistically significant linear relationship between the individual characteristics of the medical doctors and their prescription behaviour (0.54≤ r ≤0.89) as well as between the variables "quantity" and "price" (r=0.86). Particularly notable seems to be the correlation between the number of the consultations and the quantity of the prescribed drugs. The average prescription amounts to approximately 1.8 pharmaceuticals per consultation. The quantity of drugs prescribed correlates with the demand for the physician's service. Only a few general practitioners deviate from this coherence. The tendency to prescribe disproportionately expensive drugs (average costs amount to € 18.4 per drug) especially applies to those general practitioners who, in addition to their occupation as a physician, are allowed to dispense the pharmaceuticals directly to the patient within their privately owned pharmacies ("Hausapotheke"). In addition to this attribute, the variables "number of patients" and "number of consultations" intensify the effect. The risk to be identified as an outlier is 7 times higher within the group of general practitioners who own a "Hausapotheke" and account for an above average number of consultations as within the group that does not incorporate those characteristics. CONCLUSION:The strong coherence between the quantity and the demand is inherent to the health-care system and explains 79% of the variance of the prescribed quantities. Only 21% of the variance is determined by outside influences such as state of health of the patients. Physicians who have a monetary benefit from also distributing the drugs, however, enhance the prescription of high priced pharmaceuticals.