Detailed knowledge of the structure, dynamics, and interionic interactions of ionic liquids (ILs) is critical to understand their physicochernical properties. In this letter, we show that deuterium isotope effects on the chloride ion Cl-35/37 NMR signal represent a useful toot in the study of interionic hydrogen bonds in imidazolium chloride ILs. Sizable Delta Cl-35/37(H,D) values obtained for the model system 1-n-butyl-3-methylimidazolium chloride ([C(4)mim]Cl) upon deuteriation of the imidazolium C-2 and C-2,4,5 positions, of nearly 1 and 2 ppm, respectively, show that the approach can readily identify and differentiate Cl center dot center dot center dot H hydrogen bonds between the anion and cation. Our study is one of a few examples in which hydrogen-bonding in ILs has been investigated using deuterium isotope effects and, to our knowledge, the only one employing Cl-35/37 NMR to detect these interactions. The methodology described could be easily extended to the study of other systems bearing NMR-active nuclei.