Gadmen lies in the Bernese Oberland, and the Susten Pass lies on the eastern border of the municipality. It lies in the Gadmer watershed. The municipal borders stretch from the valley floor, with an elevation of , up to the nearby mountain peaks at about . It is located on the border of the Canton of Bern with the Cantons of Obwalden, Nidwalden, Uri and Valais. The neighboring municipalities are Engelberg, Wassen, Göschenen, Guttannen, Innertkirchen and Kerns.