Stream flow of the Rio Aconcagua basin (Central Chile) and its relationship with climatic variability of the ENSO was analyzed for the period 1950-2000. Linear trends of winter and summer seasons were performed. Yearly and seasonal trends were correlated with the Sea Surface Temperature (SST) index of the ENSO 3.4 zone. While 50% of the fluviometric stations had a hydrological deficit which reached 11.3%, the other 50% recorded a surplus. We found associations between the maximum mean monthly flow and El Nitio events, minimum monthly mean flow and La Nina events, and a positive correlation between the SST index and the mean monthly flow for the period.