Practice guidelines are an increasingly important means of conveying to practitioners and administrators the most appropriate methods of treating patients. Although the development of practice guidelines relies on scientific evidence, the consensus of expert opinion is an important ingredient, particularly in many key areas of clinical decision making that are insufficiently informed by experimental data. The authors review current methods in the assessment of expert opinion for practice guideline development and the problem of the lack of quantification. A new method is presented for quantification of expert opinion on surveys, and the development of expert consensus practice guidelines from the resulting data.