OBJECTIVE Sentinel node biopsy (SNB) is a surgical staging test in which sentinel nodes (SNs) undergo intensive histological analysis. SNB diagnoses early cancer spread, but can also reveal unexpected findings within the SNs. We review cases of incidental thyroid cells (TC) found in SNs from patients with oral squamous cell carcinoma (OSCC) to assess the prevalence of TC, and the clinical significance of these. METHODS Multicenter retrospective review of SNB performed for cT1-T2N0 OSCC. Incidental TC were identified by TTF-1 or thyroglobulin positivity. Anatomical location of nodes containing TC, TC morphology, and ongoing management/follow up of this incidental finding was recorded. Neck dissections performed during the same period were reviewed to establish the expected incidence of TC in neck nodes without serial sectioning analysis. RESULTS 278 SNB cases were reviewed. Ten procedures detected TC in nine patients (10/278, 3.6%). During the same time period 725 neck dissections were performed, six containing TCs (6/725, 0.8%). One patient underwent SNB twice with TC identified on both occasions. Three patients had both OSCC metastasis and thyroid cells. All SNB patients with TC identified underwent thyroid USS with no primary tumours identified. Three patients underwent thyroidectomy, in all cases no primary thyroid tumour was found. CONCLUSIONS Prevalence of incidental TC in SNs appears to be higher than that reported in neck dissections, these are not likely to be clinically relevant and can be managed on a conservative basis in the absence of clear metastatic features. METHODS Multicentre retrospective cohort study, 3 Laryngoscope, 134:1278-1281, 2024.