Bretthausen is an Ortsgemeinde – a community belonging to a Verbandsgemeinde – in the Westerwaldkreis in Rhineland-Palatinate, Germany.

The community lies in the Westerwald between Siegen and Limburg an der Lahn.

Bretthausen belongs to the Verbandsgemeinde of Rennerod, a kind of collective municipality.

Right near the community, Bundesstraßen 54, linking Limburg an der Lahn and Siegen, and 414 from Hohenroth to Hachenburg, cross each other.

The nearest InterCityExpress stop is the railway station at Montabaur on the Cologne-Frankfurt high-speed rail line.