Objective: To assess the diagnostic accuracy of ultrasound guided fine-needle aspiration biopsy (USGFNAB) in detecting malignancy of the thyroid nodule. Setting: Tertiary care academic medical center in the Philippines. Study Design: Retrospective review of patients undergoing surgery following ultrasound guided fine-needle aspiration biopsy for nodular thyroid disease. Sensitivity, specificity, positive and negative predictive values and accuracy were calculated with respect to final histology. Subjects: A total of 2,239 nodules from 1,737 consecutive patients were subjected to ultrasound guided fine-needle aspiration biopsy at Diabetes, Thyroid and Endocrine Center, St. Luke’s Medical Center. Two hundred fifty-one of the nodules were surgically excised following FNAB. Results: The USG-FNAB yielded 90.3% (n=1,721) adequate specimen and 9.7% (n=185) inadequate specimen. Cytology results were 1,448 (76%) benign, 63 (3.3%) malignant and 210 (11%) indeterminate for malignancy. Histologic examination of the 251 surgically excised nodules revealed 182 (73%) were benign and 69 (27%) were malignant. There were 11 false negative and 8 false positive FNAB cytology. The sensitivity, specificity, positive predictive value, negative predictive value and accuracy rate of USG-FNAB are 70.3%, 92.8%, 76.5%, 90.4% and 87.2%. The USG-FNAB identified malignancy in 37.7% of the cases and its yield for carcinoma is 27.5% when applied preoperatively. Conclusion: Our experience confirms that ultrasound guided fine-needle aspiration biopsy of the thyroid nodules is a powerful diagnostic tool in identifying malignant thyroid disease. Although, the diagnostic accuracy is good, the test remains limited by indeterminate and inadequate samples.