Arrien-en-Bethmale consists of the villages of Aret, Arrian, Tournac, and Villargein, all located in the Pyrenees mountains in the Bethmale valley in the former province of Couserans some 12 km south-west of Saint-Girons and 3 km south of Castillon-en-Couserans.
The Ruisseau de Cournelliere and the De Leaude rise north-east of the village and flow down to the south-west to join the Balamet river which flows down the valley to join the Lez north-west of the commune just south of Les Bordes-sur-Lez.