One application that leverages the full potential of flow chemistry is the synthesis of radiopharmaceuticals and PET tracers. Positron emission tomography (PET) has become one of the most important diagnostic methods in clinical and preclinical cancer research. It is an in vivo imaging technique that allows non-invasive visualization of biochemical processes and imaging and quantification of pathological situations in vivo by incorporating a radioactive isotope into a target molecule. Here, the synthesis of [18F]2-fluoro-2-deoxy-D-glucose ([18F]FDG), the gold standard among PET radiotracers, serves as an application example for our 3D-printed flow system.