A numerical model of lithosphere shortening has been developed to combine flexural isostatic and structural balancing. This allows us to quantitatively reconcile lithosphere shortening, thrust sheet emplacement, and foreland basin formation. Lithosphere shortening is accommodated by thrusting in the upper crust and by distributed deformation in the lower crust and the lithospheric mantle. This leads to loading by thrust sheet emplacement, crustal thickening, and thermal perturbation. Additional loading and unloading are generated by sedimentation and erosion, respectively. The model is kinematically controlled, each fault having its position, geometry, and movement prescribed. The model is applied to the Subandean late Oligocene to Recent foreland fold and thrust belt of NW Argentina at 22¿15'S. The Subandean belt of NW Argentina contains three major stratigraphic units, the Lower, Middle, and Upper Terciario Subandino Formations. By modelling these formations we attempt to determine whether the Terciario Subandino Group can be explained as a foredeep fill in response to thrust sheet loading, and, if so, what is the required effective elastic thickness. A successful model must predict not only foreland stratigraphy but also exhumation, topography, and crustal thickness. We see a change in the wavelength of sedimentary deposition in the Subandean basin through time that can be accounted for by a change in flexural rigidity. Accommodation space for the Lower Terciario Subandino Formation can be generated using an elastic thickness of 70 km. For the Middle/Upper Terciario an elastic thickness of 15 km produces the correct basin geometries. Shortening estimates of 110 km have proved sufficient to generate the observed foreland stratigraphy, Bouguer anomaly, and topography across the Subandean belt and Eastern Cordillera. However, an additional 140 km of shortening is required to generate the observed Bouguer anomaly and topography across the western Andes. This discrepancy could be due to earlier shortening in the western Andes or to crustal thickening by magma addition. ¿ American Geophysical Union 1996