Endophilin-A is a protein with a critical function in synaptic vesicle retrieval. It has a BAR domain that can change the curvature of lipid bilayers, an obligatory aspect of synaptic vesicle reformation. Detailed structure-function studies of the endophilin-A BAR domain have only been performed in vitro or in cultured cells. Here, we have analyzed the role in vivo of specific structural features of the endophilin BAR domain. We evaluated the genetic rescue of Drosophila endophilin-A (endoA) null mutants obtained with wild type or mutated endoA transgenes. We quantified viability and locomotion of the rescuants, and their neuromuscular transmission. While mutating the endophilin BAR domain reduced the performance of adult flies, larval endophilin function was resistant. EndoA carrying a charge-negative substitution that disrupts in vitro tubulation of liposomes, rescued the viability and neurotransmission with the same efficiency as wild type endoA transgenes, even in adults. A similar discrepancy between the in vitro and in vivo outcomes was found with other mutations. The A66W mutation strongly enhances the vesiculation of liposomes in vitro. We found that A66W severely impeded fly eye development, even when the endogenous endoA gene was present. Extensive structural perturbations of the central helix-loop appendage severely affected endophilin-A function. However, substantial residual function was seen in larvae rescued with EndoA(Arf), which encodes a form of endophilin-A totally lacking the appendage. A mutation designed to increase the BAR curvature, did not impede the performance of EndoA. By contrast, another mutation designed to decrease the curvature, abolished EndoA function. This study provide important novel information about the structure/function relationship of the endophilin-A BAR domain in vivo.