The Transmembrane BAX Inhibitor Motif (TMBIM) protein family consists of six evolutionarily conserved hydrophobic proteins that affect programmed cell death and the regulation of intracellular calcium levels. The bacterial orthologue BsYetJ is a pH-dependent calcium channel. We here identified six TMBIM family members in Drosophila melanogaster and studied the effect of their RNAi-mediated knockdown using ubiquitous and tissue-specific drivers. Mammalian TMBIM6 and TMBIM5 have obvious orthologs while this is more dubious for the other family members. Ubiquitous knockdown of family members dmTMBIM1,4,5, and 6 caused failed eclosing and tissue-specific knockdown resulted in a dramatically decreased lifespan. On the contrary, knockdown of dmTMBIM3, surprisingly, extended lifespan. Only knockdown of dmTMBIM6 increased the ER calcium levels of Pdf neurons. Neural knockdown of dmTMBIM2,3, and 4 increased ER stress, as indicated by increased Xbp1 splicing. Interestingly, TMBIM1 and TMBIM6 have a very similar expression pattern and their knockdown phenocopied each other. Also, knockdown of TMBIM1 resulted in upregulation of TMBIM6 and vice versa further suggesting a genetic interaction between these two genes. Our data demonstrate that most TMBIM proteins are essential for fly development and survival but, despite their shared protein structure, affect cell survival through different mechanisms.