In the search for effective radiosensitizers for tumor cells, halogenated uracils have attracted more attention due to their large cross section for dissociation upon the attachment of low-energy electrons. In this study, we investigated dissociative electron attachment (DEA) to 5-iodo-4-thio-2'-deoxyuridine, a potential radiosensitizer using a crossed electron-molecule beam experiment coupled with quadrupole mass spectrometry. The experimental results were supported by calculations on the threshold energies of formed anions and transition state calculations. We show that low-energy electrons with kinetic energies near 0 eV may effectively decompose the molecule upon DEA. The by far most abundant anion observed corresponds to the iodine anion (I-). Due to the associated bond cleavage, a radical site is formed at the C5 position, which may initiate strand break formation if the molecule is incorporated into a DNA strand. Our results reflect the conclusion from previous radiolysis studies with the title compound, suggesting its potential as a radiosensitizer.