In this paper we analyse the discrepancies that exist in the widespread prescription of metformin in patients with type 2 diabetes and the lack of guidelines concerning its prescription in the different stages of renal failure. This cross-sectional study includes 304 patients with type 2 diabetes treated with oral antidiabetic drugs (ADOs) and a glomerular filtration rate (estimated GFR) <60ml/min/1.73m2. Patients were attended in consecutive visits to primary health centres or in hospital departments of endocrinology or nephrology during 2010. We studied the frequency of metformin and other ADO prescriptions according to renal function and the department in which the patient was treated. The ADO most frequently prescribed was metformin (54.9%), followed by repaglinide (47.7%), DPP4 inhibitors (28.6%), and sulfonylureas (18.4%). However, in nephrology departments, repaglinide was more frequently prescribed than metformin (P<.001), whereas in primary health centres, the prescription of DPP4 inhibitors increased. In patients with an estimated GFR of 15-29ml/min/1.73m2, metformin (13.3%) and sulfonylureas were the least prescribed, whereas metformin was much more frequently prescribed (70.0%) when estimated GFR was 45-59ml/min/1.73m2 (P<.001). In contrast, patients with an estimated GFR of 15-29ml/min/1.73m2 were mainly prescribed repaglinide (76.7%), as opposed to patients with an estimated GFR of 45-59ml/min/1.73m2 (38.9%) (P<.001). Substantial evidence suggests that the recommendations for the use of ADO should be modified. This would lead to safely prescribing ADO in patients with an estimated GFR<60ml/min/1.73m2, and more importantly in medical practice, according to the law.