In the work reported here the comprehensive physics-based Integrated Hydrology Model (InHM) was employed to conduct both three- and two-dimensional (3D and 2D) hydrologic-response simulations for the small upland catchment known as C3 (located within the H. J. Andrews Experimental Forest in Oregon). Results from the 3D simulations for the steep unchannelled C3 (i) identify subsurface stormflow as the dominant hydrologic-response mechanism and (ii) show the effect of the down-gradient forest road on both the surface and subsurface flow systems. Comparison of the 3D results with the 2D results clearly illustrates the importance of convergent subsurface flow (e.g. greater pore-water pressures in the hollow of the catchment for the 3D scenario). A simple infinite-slope model, driven by subsurface pore-water pressures generated from the 3D and 2D hydrologic-response simulations, was employed to estimate slope stability along the long-profile of the C3 hollow axis. As expected, the likelihood of slope failure is underestimated for the lower pore pressures from the 2D hydrologic-response simulation compared, in a relative sense, to the higher pore pressures from the 3D hydrologic response simulation. The effort reported herein provides a firm quantitative foundation for generalizing the effects that forest roads can have on near-surface hydrologic response and slope stability at the catchment scale. Copyright © 2006 John Wiley & Sons, Ltd.