The purpose of this report is to provide an evaluation of the impact of supplementary irrigation in grain production in the northern area of the Province Buenos Aires, Argentina within the framework of risk analysis and with emphasis on risk related to weather. An economic analysis of a productive model in the mentioned area, characterized by fertile soils and considering a farm of 400 hectares destined integrally to the production of grains is carefully developed. This analysis clearly shows that the main impact of supplementary irrigation is associated with the reduction of variability in yields and with the increase of expected farm income and net revenue. The rate of return on investment on irrigated agriculture more than doubles the one related to rainfed agriculture. Acknowledgement : My name is Anibal Leandro Nu ez, argentinean economist finishing the studies of magister in agrarian economy (Universidad de Buenos Aires). I am currently working in the Ministery of Agro-industry. The work was done in conjunction with Dr. Raul Fiorentino (Ph.D University of California in Davis), who also works in the Ministery of Agro-industry. The purpose of this report is to provide an evaluation of the impact of supplementary irrigation in grain production in the northern area of the Province Buenos Aires, Argentina within the framework of risk analysis and with emphasis on risk related to weather.