El Niño-Southern Oscillation (ENSO) exerts a strong influence on agriculture through its influence on climate. In south-eastern South-America El Niño signal is related to increments in winter temperatures and higher precipitations during the "season" November-February. Inversely, La Niña events are related with negative anomalies in winter temperatures and precipitation values lower than normal during the "season" June-December. Results obtained for the Pampas region in Argentina, demonstrated that in Niño years precipitations tend to be higher than normal values, in particular between November and January, but in Niña years they tend to be lower than normal between October and December. Inter-annual and inter-seasonal climatic fluctuations cause high variability in crop production, with varied consequences on food supply and economics. Mean annual grain production in the Pampas amounts 35 Mtn, but it can vary from 21 Mtn to 55 Mtn under the worst or best situation respectively. The most important contributors to Argentina´s national grain production are wheat, maize, soybean and sunflower crops. Impacts of climatic variability related to ENSO on crop production should be different depending on the phase but also on the crop involved. To quantify these impacts on wheat, maize, soybean and sunflower production in the Argentina’s Pampas Region, historical yields and not harvested areas were analysed. For this purpose ENSO phases were categorised following JMA definition. At the national level, in 75% of Niño events maize yield was equal or higher than the mean value, while in 74% of Niñas it was lower than the mean. In soybean a greater impact was associated with Niña years, where yield reductions were observed in 71% of them. Sunflower had an opposite behaviour, in 59% of Niña years yields were higher than the mean. Little response was observed in wheat. Analysis of grain yields at county level allowed to detect zones with differential response to ENSO phases. During Niño years maize yields were higher in the south-southeast of the Pampas Region but in Niña events they were considerably reduced in the main production zone. Soybean showed lower yields all over its main production area during Niña years, while higher yields under Niño events were found only in isolated areas. Higher and lower wheat yields were observed during Niño and Niña years in the south-west zone which is an important contributor to planted area. Sunflower evidenced important yield reductions during Niño years in the main production zone but yield increments in the opposite phase occurred in some counties. For most of the region yield variability related to ENSO phases was associated with the occurrence of precipitations higher than normal (Niños) or lower than normal (Niñas) during critical growth periods, except for sunflower. ENSO impact on not harvested areas was strongly evidenced in maize; in 87% of counties not harvested areas during Niña events were significantly higher than those from Niño years