Langerhans cells (LCs) are dendritic cells (DCs) residing in epithelia, where they critically regulate immunity and tolerance. The p14 adaptor molecule is part of the late endosomal/lysosomal adaptor and MAPK and mTOR activator/regulator (LAMTOR) complex, thereby contributing to the signal transduction of the "extracellular signaling-regulated kinase" (ERK) and the "mammalian target of rapamycin" (mTOR) cascade. Furthermore, p14 represents an important regulator for endosomal sorting processes within the cell. Mutated, dysfunctional p14 leads to a human immunodeficiency disorder with endosomal/lysosomal defects in immune cells. Since p14 participates in the regulation of endosomal trafficking, growth factor signaling and cell proliferation, we investigated the role of p14 in mouse DCs/LCs using a conditional knock out mouse model. p14-deficient animals displayed a virtually complete loss of LCs in the epidermis early after birth due to impaired proliferation and increased apoptosis of LCs. Repopulation analysis after application of contact sensitizer leads to the recruitment of a transient LC population, predominantly consisting of short-term LCs. The underlying molecular mechanism involves the p14-mediated disruption of the LAMTOR complex which results in the malfunction of both ERK and mTOR signal pathways. Hence, we conclude that p14 acts as a novel and essential regulator of LC homeostasis in vivo.