Diegem is a town in the municipality of Machelen, in the province of Flemish Brabant, Belgium. Diegem's postal code is 1831. The official language of Diegem is Dutch, as in the rest of Flanders. A portion of Brussels Airport is located in Diegem, together with neighbouring town of Zaventem. Diegem's situation just outside the Brussels-Capital Region and close to the R0 also means it has a large number of business premises.