Introduction Thyroid fine needle aspiration (FNA) is one of the most commonly performed diagnostic procedures in out- patient departments. 1,2 It is quick, cost-effective, and minimally invasive technique which reduces the need for an un-necessary surgery. 3 FNA has been recommended as initial diagnostic test in the evaluation and management of thyroid nodules, having sensitivity and specificity of 95% and 90% respectively. 4 Previously, pathologists have been using variable terminologies for cytological reporting of thyroid lesions which were all ambiguous and inconsistent. Different reporting criteria were used in different laboratories. The results didn't show proper clinical relevance and created confusion among pathologists, endocrinologists, surgeons and radiologists. 5,6 National Cancer Institute, Bethesda, USA, after holding a series of conferences and discussions, introduced the Bethesda Reporting System in 2007, 7 which established a six-tier classification system for reporting thyroid lesions. It was expected to provide standardised framework for laboratory reports which would reduce confusion among different healthcare providers. It was to enable pathologists to diagnose thyroid lesions as distinct entities according to accepted criteria and provide clear guidance for clinical management. 8 Moreover, it will also help in the prospective research work related to thyroid malignancies. 9 The purpose of this study was to evaluate Bethesda Classification for reporting thyroid by recording interobserver reproducibility. To the best of our knowledge, it is the first study done in Pakistan in which interobserver agreement for Bethesda System was analysed. Patients and Methods A total of 200 thyroid FNA cases were retrieved from the archives from 2009 to 2011 at the Pathology Department of Foundation University Medical College, Islamabad. All cases were independently reviewed by 3 histopathologists and were placed into 6 categories: Non-diagnostic/ Unsatisfactory ND' (category-1), Benign B' (category-2); Atypia of undetermined significance/Follicular Lesion of Undetermined Significance 'AUS/FLUS' (category-3), Follicular Neoplasm/Suspicious for Follicular Neoplasm 'FN/SFN' (category-4); Suspicious for malignancy 'SFM' J Pak Med Assoc 1252 ORIGINAL ARTICLE The interobserver reproducibility of thyroid cytopathology using Bethesda Reporting System: Analysis of 200 cases Safina Ahmed, 1 Mumtaz Ahmad, 2 Masood Ahmad Khan, 3 Faiza Kazi, 4 Fozia Noreen, 5 Samia Nawaz, 6 Iram Sohail 7 Abstract Objective: To determine interobserver reproducibility of thyroid cytopathology in cases of thyroid fine needle aspirates. Methods: The retrospective, descriptive study, was conducted at the Foundation University Medical College, Islamabad, using cases related to period between 2009 and 2011. A total of 200 cases of fine-needle aspirations were retrieved from the archives. Three histopathologists independently categorised them into 6 groups according to Bethesda reporting system guidelines without looking at previous reports. Kappa statistics were used for analysis of the results on SPSS 17. Results: Of the 200 patients, 194 (97%) were females and 6 (3%) were males. The overall mean age of patients was 46±20 years. Kappa value calculated for observer-1 and observer-2 was 0.735; for observer-1 and observer-3, 0.841; and for observer-2 and observer-3, 0.838, showing substantial interobserver agreement. Histopathological correlation was available, for 39(19.5%). Of these cases, 5(13%) were 'non-diagnostic, 20(51%) 'benign, 2(5%) 'atypia of undetermined significance/follicular lesion of undetermined significance, 6(15%) 'follicular neoplasm, 1(3%) 'suspicious for malignancy, and 5(13%) 'malignant. Conclusions: Good overall interoberver agreement was found, but discordance was seen when certain categories were analysed separately. Keywords: Thyroid, Fine-needle aspiration, Bethesda System, Interobserver reproducibility. (JPMA 63: 1252; 2013) 1-4 Department of Pathology, 5-7 FCPS II trainee, Foundation University Medical College, Islamabad. Correspondence: Safina Ahmed. Email: a_safina@yahoo.com