Amyloid-β 1-42 (Aβ1-42) measured in the cerebrospinal fluid (CSF) can be used as a diagnostic biomarker for Alzheimer's disease (AD) but an upward drift when using the INNOTEST ELISA has been suggested. We investigated the upwards drift of Aβ1-42 levels over a period of twelve years in a consecutive memory clinic cohort. We found a significant increase in Aβ1-42 from 2008 to 2019 independent of changes in tau. New methods for the quantification of CSF Aβ1-42 levels are being implemented but awareness of this upwards drift is crucial during the diagnostic work-up and when selecting historical samples for research.