The 2003 Common Agricultural Policy (CAP) reform consti-tutes a reinforcement of the main objectives of the previous reforms of 1992 and of 2000, namely the promotion of the agricultural competitive-ness, the multiple functions of the rural and agricultural areas and the sustainable resource exploitation. The direct production aids in the most Common Market Organizations are replaced by an only payment for each farm, subject to echo-conditionality and limits on the agricultural systems changes. This article evaluates the impacts of 2003 CAP reform on the Portugal irrigation competitiveness in the Alentejo region farms. The effects of the only payment in the agricultural returns, the main changes in the crop patterns and in the agricultural incomes were studied. They are also appraised direct social economic and environmental impacts of the adjustments produced with the 2003 CAP reform. The followed methodology is a discreet stochastic programming model. This model maximizes the expected income and minimizes the risk at the farm level. It was used to assess the crop patterns and the farm inco-me in the short and in the long term, in the scenarios of the 2000 CAP and the of the 2003 CAP.