The aim of this two-step randomized study carried out in Wallonia, Belgium, was to analyse the behaviour of general practitioners in prescribing drugs to the elderly (>75 years). Consumption of drugs by old people is often claimed to be too high and not always medically necessary but it is also recognized that the elderly are inclined to suffer from several diseases simultaneously. The study sample yielded information on 355 general practitioners, 3,384 patients (9.5 patients per doctor) and 16,117 drugs (4.7 drugs per patient). Overall, drug prescription to the elderly in Wallonia was higher than that reported for other countries. Cardiovascular diseases were the major reason for drug prescription. Tranquillizers and hypnotics were prescribed to 34 and 35% of the patients respectively. Drug prescription patterns were analysed with respect to both doctor and patient characteristics. The mean number of drugs prescribed by doctors increased linearly (r=0.54, p<0.001) with the mean number of presenting diseases of the patients (2 drugs per disease). When accounting for this relationship, prescription patterns differed between provinces (p<0.05) and varied significantly (p<0.01) according to the university training received. The study highlights subregional differences in drug prescription and it stresses the need for adequate education of medical students in geriatric medicine.