A process is provided for manufacturing an exhaust gas treatment device (1), which contains at least one exhaust gas treatment insert (2) in a tubular housing (4), especially for an exhaust system of an internal combustion engine. A circumferential geometry of the at least one insert (2) is measured in at least one axial section of the particular insert (2). The at least one insert (2) is inserted axially into the housing (4). The measured circumferential geometry of the at least one insert (2) is taken into account during the deformation of the housing (4).