Westrehem () is a commune in the Pas-de-Calais department in the Hauts-de-France region of France about west of Béthune and southwest of Lille.
It is surrounded by the communes of Ligny-lès-Aire, Fontaine-lès-Hermans and Febvin-Palfart. Westrehem is located 16 km northwest of Bruay-la-Buissière, the largest nearby city.