Purpose: Thyroid surgery is commonly performed for nodules deemed low-suspicion on ultrasound (US) for compressive symptoms, thyrotoxicosis or interval growth. Published false-negative (FN) rates for benign cytology vary widely (5% to >20%). A 2025 meta-analysis demonstrated FN rates of 5.3-6.9% across over 5000 nodules.2 We aimed to identify the number of clinically significant malignancies on final histology among presumed benign nodules in a West Australian cohort. Methodology: Adults (≥18 years) who underwent thyroid surgery for benign appearing lesions (Jan 2020–Nov 2025) were identified from a database. Baseline data including sex, age, history of neck irradiation and indication for surgery was collected. Patients with benign cytology and available final histology were included. US features including size, echotexture, vascularity and presence of microcalcifications were extracted from radiology reports. Histology was recorded postoperatively. Statistical analysis was performed using R. Results: 711 patients underwent surgery for benign indications. Radiology reports were available for 396 patients. Twenty patients received a post-operative histological diagnosis of clinically significant carcinoma (>1cm). The false negative rate for combined US and FNA was 5.1% (20/396). The presence of microcalcifications on US was the strongest predictor of malignancy in the group (OR 6.55, 95% CI 2.11-20.03, p=0.01). Conclusion: In this Western Australian cohort, benign preoperative assessment with US and FNA was associated with a 5.1% false negative rate, with microcalcification on US as the strongest predictor of malignancy. This data is in keeping with level I evidence. References: 1) Cotter A, Jinih M. Discov Oncol. 2025;16:1188