Until now, there has been no uniform system for reporting the results of thyroid fine needle aspiration (FNA) in the U.S. The terminology framework described in this book is an important advance in the field of cytopathology. It is a brainchild of the multidisciplinary National Cancer Institute Thyroid Fine Needle Aspiration State of The Science Conference, held in Bethesda, MD in October, 2007. This book will provide the reader with a unified approach to diagnosing and reporting thyroid FNA interpretations. It will serve as a reference guide not just for pathologists, but also endocrinologists, surgeons, and radiologists. Thyroid FNA is one of the most commonly performed cytologic procedures and is the standard diagnostic method for managing the patient with a thyroid nodule. In the past, ambiguous and inconsistent diagnostic criteria and terminology have hampered sample interpretation and patient management. It is hoped that, by bringing together national and international thyroid experts from diverse disciplines, the book will achieve its goal: to provide the reader with a generously illustrated and user-friendly reference on this unified approach to thyroid diagnostic criteria and reporting. The book will succinctly summarize and illustrate the salient points in the diagnosis of the non-neoplastic and neoplastic thyroid diseases. The chapters will be set up as follows: 1. Background, 2. Criteria, 3. Explanatory Notes, and 4. Sample reports. The development of the Bethesda System for Thyroid FNA parallels the development of the Bethesda System for Reporting Cervical Cytology, which was also the result of an NCI-sponsored multidisciplinary conference. Now in its 2nd edition (Solomon and Nayar, 2004, Springer), "The Bethesda System for Reporting Cervical Cytology" revolutionized the reporting of Pap test results. Virtually every cytopathology laboratory in the U.S. (and a large number overseas) uses the Bethesda System for reporting Pap test results and thus owns at least one copy of the book. The new terminology has already received much attention in the planning of upcoming national and international meetings. We expect that the Bethesda System for thyroid FNA will have the same effect in transforming, unifying, and improving the reporting of thyroid FNA results as its sister publication did for Pap testing.