Microscopic analysis of molecules and physiology in living cells and systems is a powerful tool in life sciences. While in vivo subcellular microscopic analysis of healthy and diseased human organs remains impossible, zebrafish larvae allow studying pathophysiology of many organs using in vivo microscopy. Here, we review the potential of the larval zebrafish pancreas in the context of islets of Langerhans and Type 1 diabetes. We highlight the match of zebrafish larvae with the expanding toolbox of fluorescent probes that monitor cell identity, fate and/or physiology in real time. Moreover, fast and efficient modulation and localization of fluorescence at a subcellular level, through fluorescence microscopy, including confocal and light sheet (single plane illumination) microscopes tailored to in vivo larval research, is addressed. These developments make the zebrafish larvae an extremely powerful research tool for translational research. We foresee that living larval zebrafish models will replace many cell line-based studies in understanding the contribution of molecules, organelles and cells to organ pathophysiology in whole organisms.@en