Background There is limited published data on the stability of calcitonin, chromogranin A, thyroglobulin and anti-thyroglobulin antibodies in serum. The aim of this study was to determine stability at three temperature conditions over 7 days, reflecting current laboratory practices. Methods Surplus serum was stored at room temperature, refrigerated and in the freezer; for 1, 3, 5 and 7 days. Samples were analysed in batch and analyte concentrations compared to that of a baseline sample. Measurement Uncertainty of the assay was used to determine the Maximal Permissible Difference and thus the stability of the analyte. Results Calcitonin was found to be stable for at least 7 days in the freezer but only 24 h refrigerated. Chromogranin A was stable for 3 days when refrigerated and only 24 h at room temperature. Thyroglobulin and anti-thyroglobulin antibodies were stable under all conditions for 7 days. Conclusion This study has enabled the laboratory to increase the add-on time limit of Chromogranin A to 3 days, and up to 60 min for calcitonin and inform optimal storage and transportation conditions for referring specimens.