There are multiple practice guidelines published pertaining to diabetes care. Experts have formulated methodologic standards of guideline formulation. To determine whether practice guidelines pertaining to diabetes and published in peer-reviewed publications and the Internet adhered to established methodologic standards of guideline development. We identified all guidelines pertaining to diabetes care published between 1980 and 2000 using a computerized search of Medline, the Practice Guidelines Clearinghouse, the Institute for Clinical Systems Improvement Web site, and a global internet search engine. We used a previously validated 25-item assessment tool to determine guideline adherence to methodologic standards in three categories: guideline development and format, identification and summary of evidence, and formulation of recommendations. We conducted a multivariable regression analysis to determine the influence of guideline author, publishing medium, year of publication, and guidelines length on adherence to methodologic standards of guideline development. We evaluated 43 guidelines: 33% published on the Internet, 66% in peer-reviewed journals; 51% published by organizations, and 49% by individual experts. Of a maximum of 25 methodologic standards, the number of standards adhered by a guideline was 9 (range, 2 to 19). Mean proportion (SD) of guidelines that adhered to methodologic standards on guideline development and format was 48% (28); on identification and summary of evidence, 21% (22); and on the formulation of recommendations, 36% (27). Longer guidelines had greater adherence to methodologic standards (P < 0.0001). Guidelines pertaining to diabetes care published on the internet and in peer-reviewed publications do not meet most methodologic standards of guideline development.