Humanin (HN) is a 24-residue peptide displaying a protective activity in vitro against a range of cytotoxic and neurotoxic insults, as well as mediating in vivo amelioration of Alzheimer disease (AD)-related memory impairment in experimental models. Published evidence suggests that the mechanisms through which HN exerts its cyto- and neuroprotective activity may include its secretion and binding to membrane-associated receptors. Here, we describe the identification of a new modulator of HN neuroprotective activity, V-set and transmembrane domain containing 2 like (VSTM2L), previously known as C20orf102. VSTM2L interacts with HN in both yeast and mammalian cells, is secreted in cultured cells, is present in serum, and is selectively expressed in the central nervous system. VSTM2L colocalizes with HN in distinct brain areas as well as in primary cultured neurons, where it plays a role in the modulation of neuronal viability. When tested in HN neuroprotection bioassays, VSTM2L acts as a strong antagonist of HN neuroprotective activity. In summary, VSTM2L is the first example of a secreted antagonist of HN and may play a role in the modulation of HN biological functions.