Objectives: The storage of serum tumor markers (STM) at -18 °C for one year has been a legal requirement in France since 1999, but has been abolished in 2022. This raises the question of the relevance of maintaining these biobanks in terms of conditions of storage. These should only be implemented after validation; in order to maintain the integrity of the biological sample and must be controlled over time according to the laboratory's procedures. The aim of the study was to assess the suitability of storing 10 STMs by evaluating their stability after one year of storage at -18 °C., Methods: A new immuno-enzymatic assay (A+1) was conducted on samples that had been stored at -18 °C for one year after an initial assay (A) of one of the following STMs: carcino-embryonic antigen (CEA), alpha-fetoprotein (AFP), carbohydrate antigen 125 (CA125), carbohydrate antigen 15-3 (CA15-3), carbohydrate antigen 19-9 (CA19-9), total (TPSA), and free (FPSA) prostate-specific antigen, calcitonin (CT), thyroglobulin (TG), and neuro-specific enolase (NSE). The results were confronted to four different permissible error sources., Results: In total, 1148 A+1 assays were performed. A strong correlation between A+1 and A values was found for all analytes, but with a statistically significant reduction in the mean A+1 concentration compared to the mean A concentration in 7/10 STMs. The bias induced by conservation seems to be technically unsustainable if we rely on the repositories closest to the current analytical performances., Conclusions: These results support the discontinuation of mandatory STM biobank storage at -18 °C, which requires considerable technical time and organizational effort., (© 2024 Walter de Gruyter GmbH, Berlin/Boston.)