Inkjet printing is a nascent technology that is developing from only printing text and graphics into a major topic of scientific research and R&D, where it can be used as a highly reproducible non-contact patterning technique to print at high speeds either small or large areas with high quality features. Inkjet printing is an additive technique, which requires only small amounts of functional materials, which can vary from a simple polymer solution to advanced nanoparticle dispersions. The latter form of ink has been investigated more and more during the last few years, in order to produce conductive features that require a reduced amount of processing steps.In recent years inkjet printing has been used for the production of microelectronic structures on (flexible) substrates and for the rapid production of 2D and 3D microstructures. In order to create these microstructures we present ‘reactive inkjet printing’ as a technology to create micron-scale polyurethane structures, such as dots, lines and pyramids. These structures were fabricated in-situ and cured within five minutes by inkjet printing successively two separate inks respectively from two separate print heads, with one ink containing isophorone diisocyanate, and the other consisting of an oligomer of poly(propylene glycol), a catalyst, and a cross-linking agent. The fast polymerisation reaction that forms polyurethane at the surface opens a new route for rapid prototyping, as well as the use of inkjet as a technique for handling moisture-sensitive reactions.