Practice guidelines have proliferated in medicine but their impact on actual practice and outcomes is difficult, if not impossible, to quantify. Though guidelines are based largely on observational data and expert opinion, it is widely believed that adherence to them leads to improved outcomes. Data to support this belief simply does not exist. If guidelines are universally ignored, their impact on treatment and outcomes is minimal. The incorporation of guidelines into treatment protocols and performance measures, as is now common practice in nephrology, increases greatly the likelihood that guidelines will influence practice and hence, outcomes. Practice patterns set up this way may be resistant to change, should new evidence emerge that contradicts certain recommendations. Even if guidelines are entirely appropriate, a ‘one-size-fits-all’ approach is likely to benefit some, but not all. Certain patients may be harmed by adherence to specific guidelines. Guidelines certainly do not encourage clinicians to consider and treat each patient as an individual. They are unlikely to stimulate original research. They are created by a process that is artificial, laborious and cumbersome. This all but guarantees many guidelines are obsolete by the time they are published. Guidelines are produced with industry support and recommendations often have a major impact on sales of industry products.