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Live observation of biological phenomena in the context of living organisms can provide important insights in the mechanisms of these phenomena. However, the spatially complex and dynamic physiology of multicellular organisms can be a challenging environment to make observations with fluorescence microscopy. Due to the illumination of out-of-focus planes, confocal and particularly widefield fluorescence microscopy suffer from low signal-to-background ratio (SBR), photo toxicity and bleaching of fluorescent probes. In light-sheet microscopy (LSM), solely the focal plane of the detection objective is illuminated, minimising out-of-focus fluorescence and photobleaching, thereby enhancing SBR, allowing for low laser intensities and longer acquisition periods. Here we present a straightforward light-sheet microscope with a 1.0-NA detection objective and a fast sample-positioning stage that allows for four degrees of freedom. By imaging the sensory cilia and nervous system of living young adult C. elegans, we demonstrate that the instrument is well suited for relatively fast, volumetric imaging of larger (hundreds of micrometres cubed) living samples. These experiments demonstrate that such an instrument provides a valuable addition to commonly used widefield and confocal fluorescence microscopes. LAY DESCRIPTION: In fluorescence microscopy, sharp images can only be obtained when the light obtained from the section of the image that is in focus is not overwhelmed by light emerging from elsewhere. In this paper, we present a light-sheet fluorescence microscope, based on the OpenSPIM initiative, with a magnification of 90× and a sensitive sample positioning stage that allows for fast controlled linear movement and rotation. In a light-sheet microscope (LSM), the sample is illuminated from the side, compared to the direction of detection, limiting illumination only to the part of the sample that is imaged in the focal plane (general resources: Wikipedia or MicroscopyU). This does not only limit background noise, but also reduces damage to the sample due to phototoxicity. This makes a LSM particularly suitable for imaging living samples at high resolution, in three dimensions, over long periods of time. Our instrument was specifically designed for imaging adult C. elegans nematodes. We show here how the instrument compares to a standard epifluorescence microscope, imaging neuronal structures in the animals. The instrument proved well suited for fast volumetric imaging of larger cellular structures such as C. elegans neuronal cell bodies. Our experiments show that the instrument provides a valuable addition to widefield and confocal fluorescence microscopes commonly used to image adult C. elegans., (© 2020 The Authors. Journal of Microscopy published by John Wiley & Sons Ltd on behalf of Royal Microscopical Society.)