In order to circumvent these inherent limitations, we propose the use of positron emission tomography (PET) as an alternative to fluorescence‐based assays.16 Previous attempts to develop ALDH1A1‐specific radiotracers have so far failed due to the poor cellular retention of the carboxylate product, presumed to be a consequence of its high hydrophobicity.17 Here, we report the synthesis and biological evaluation of 18F‐fluorinated aldehyde‐based probes for the non‐invasive detection of ALDH1A1 activity in tumor cell models. This evidence concerns the gene ALDH1A1 and neoplasm.