This study applies systems simulation to characterize determinants of sustainability of a hillside farm in the upper Cauca River watershed of Colombia. A farm model linked to process-level crop models was used to simulate a set of farm scenarios. Susta inability, expressed as the probability of farm continuation, was estimated for each scenario based on replicated simulation with stochastic weather and price inputs. Hypotheses about determinants of sustainability were tested by sensitivity analysis. Res ults identify cropping system, area under cultivation, consumption requirements and crop prices as important determinants of sustainability. The study highlights the impacts of price variability and spatial diversification on farm risk and the results sug gest ways to enhance the sustainability of the farm. The methodology was useful for integrating the diverse biophysical and economic factors that affect farm sustainability.