Objective: To evaluate the quality of orders for target drugs in old patients with impaired renal function, hospitalized or living in long stay units, and to improve these practices by means of counselling system coupled to a computer prescribing system. The computer prescribing system allow (a) to detect in real-time the order of drugs contraindicated in case of renal failure or prescribed in excessive amount taking into account the creatinine clearance (ClCr), and (b) to counsel the physician in these situations.