The Coulomb critical taper model has been very successful in explaining the large-scale topography of a number of terrestrial accretionary wedges; however, this model is limited to cases of purely brittle-friction deformation. In this paper we extend the range of applicability of the critical taper model by explicitly including the effects of temperature-dependent ductile deformation. The new model includes temperature-dependent power law flow, an assumed velocity field, and linear thermal gradients in the atmosphere and within the crust. Flexural isostasy is also incorporated so that the decollement geometry is computed as a response to the applied load of the wedge material. We assume that ductile deformation within the decollement zone is controlled primarily by diffusion flow, whereas ductile deformation within the wedge itself is controlled by dislocation creep. The topographic profiles predicted by the model are very similar to those of a number of fold-and-thrust belts on both Earth and Venus. A typical wedge profile includes three distinctive topographic regions: a narrow taper toe, where both the wedge and the decollement zone deform in a brittle-frictional manner; a region of relatively steep slope, where the wedge base deforms ductilely and the decollement zone is still frictional; and a flat plateau region, where both the wedge base and the decollement zone are deforming by ductile flow. We have applied the model to two fold-and-thrust belts on Venus (Maxwell Montes and Uorsar Rupes) and to the Andes on Earth, and we find good agreement between observed and predicted topography using reasonable parameter values. The model accounts for the observed positive correlation between relief and elevation of Venusian fold-and-thrust belts on the basis of different thermal environments at different elevations. It is also able to explain the first-order differences between terrestrial and Venusian fold-and-thrust belts; fundamentally, this difference is due to a combination of the lower temperatures and the presence of water on Earth. ¿ American Geophysical Union 1994