For the past decade, the emerging class of porous metal-organic frameworks has been becoming one of the most promising materials for the construction of extralarge pore networks in view of potential applications in catalysis, separation and gas storage. The knowledge of the atomic arrangements in these crystalline compounds is a key point for the understanding of the chemical and physical properties. Their crystal size limits the use of single-crystal diffraction analysis, and synchrotron radiation facilities may allow for the analysis of tiny crystals. We present here a microdiffraction set-up for the collection of Bragg intensities, which pushes down the limit to the micrometre scale by using a microfocused X-ray beam of 1 mum. We report the structure determination of a new porous metal-organic-framework-type aluminium trimesate (MIL-110) from a single crystal of a few micrometres length, showing very weak scattering factors owing to the composition of the framework (light elements) and very low density. Its structure is built up from a honeycomb-like network with hexagonal 16 A channels, involving the connection of octahedrally coordinated aluminium octameric motifs with the trimesate ligands. Solid-state NMR (27Al,13C,1H) and molecular modelling are finally considered for the structural characterization.