The development of recommendations for what is acceptable clinical practice for patients with adult periodontitis is challenging. First, how much and what type of evidence is needed? This depends very much on the clinical problem, the nature of the evidence that is available, and the potential ill effects that may ensue if the effects of the treatment that is recommended are not what they are hoped to be. All treatments are applied with the implicit assumption that they do more good than harm. Treatments that are expensive, invasive, irreversible, or potentially risky, require more evidence than treatments that are not invasive, have reversible effects, and are without risk. Recall the hierarchy of types of evidence used in the AHCPR pain guidelines ranging from a meta-analysis of RCTs to uncontrolled observations in patients or expert opinion. A randomized controlled trial, or a meta-analysis of RCTs carries more weight than a much larger series of cases because of the great potential for bias when observations are made under uncontrolled conditions. One hundred poorly controlled studies do not provide evidence for optimal clinical decisions. Second, who bears the burden of proof? Certainly, any newly proposed therapy must be proven safe and effective by its proponents. But, what about treatments that have been the standard of practice, can they be grandfathered in, or must evidence be gathered for them? Given changes in understanding of mechanisms of disease pathogenesis, classification, rates of activity, and measurement of outcomes, it may be time to call all clinical dogma regarding treatment of adult periodontitis into question. Reliable evidence is not available for many of the treatments for adult periodontitis. Most of the evidence that is available was collected using methods and an underlying conceptual scheme regarding diagnosis and progression of disease that is very different from current beliefs. One could argue that even for the treatments that have been evaluated in RCTs, disease activity rates were so low by current assessment, that there was no disease to prevent or treat.