We estimate a distance function of grains production using generalized method of moments that enables us to accommodate multiple outputs of farmers as well as address the endogeneity issues that are related with the use of distance functions for multi-output production. Using a panel data set of Ethiopian subsistence farmers, we find that the most important factors determining farmers' efficiency in Ethiopia are having access to the public extension system, participation in off-farm activities, participation in labor sharing arrangements, gender of the household head, and the extent to which farmers are forced to produce on marginal and steeply sloped plots. Average farmers in Ethiopia are producing less than 60% of the most efficient farmers. Annual technical change between 1999 and 2004 is about one percent while annual efficiency change during the same period is insignificant.