The Western or Little Dender is 22 kilometres (14 miles) long and begins in Barry near Leuze-en-Hainaut at an elevation of about 60 to 70 metres (200 to 230 ft) above sea level.

It begins as several canals in the fields merging together to form the Little Dender.

The source of the Eastern Dender, which is 39 kilometres (24 miles) long, is near Jurbise at a height of 100 metres (330 feet) above sea level.

From Ath, the Dender passes into the Denderstreek through the cities and towns of Geraardsbergen, south of which its tributary, the Mark, flows into it.

From this confluence, the river continues to flow through Ninove, Denderleeuw, and Aalst, before ending in Dendermonde.