Diegem is a town in the municipality of Machelen, Flemish Brabant, Belgium.

Its gothic church, inaugurated in 1543, in the centre of town, has a conspicuous tiered spire.

The town is served by Diegem railway station, which is situated on the Brussels - Leuven railway line between Haren Zuid and Zaventem stations.

Diegem's situation just outside the Brussels-Capital Region and close to both Brussels Airport in Zaventem and the R0 (the Brussels orbital motorway) mean it has a large number of business premises.

Its postal code is 1831.