The Armuthsbach is an 18.4-kilometre-long, orographically left-hand tributary of the Ahr in the German states of North Rhine-Westphalia and Rhineland-Palatinate.

The Armuthsbach rises about 1.5 km southwest of Tondorf at a height of 531 m above sea level (NHN).

About 800 metres west of Schuld the Armuthsbach empties into the Ahr from the left at an elevation of 245 m above NHN.

Its catchment area covers 60.526 km2 and its waters drain via the Ahr and Rhine into the North Sea.

The following table lists the tributaries of the Armuthsbachs as they are recorded in the waterbody index of the state of North Rhine-Westphalia.