A long-term high quality precipitation database has been developed to assess the changing climate of Mexico during the instrumental period. Time-series with more than thirty years of information and less than ten percent of missing data were accepted for the extraction. Day to day data comparisons were made among the different constituent databases used in the development. The final network used in this study has 175 stations (168 in Mexico and 7 in the USA) with monthly rainfall from 1931 to 2001, i.e., 71 years of precipitation data. Oblique-rotated Principal Component Analysis (PCA) has been applied to the monthly dataset to regionalise groups of stations that vary coherently. Linear (Kendall’s tau-b) correlations have been applied to establish relationships between three different ENSO indices and the regional precipitation averages (resulting from PCA). A clear latitudinal transition is observed when the annual and rainy (May-Oct) seasons for the regional precipitation averages and derived extreme rainfall indices are correlated with the ENSO indices: wetter conditions are observed north of the Tropic of Cancer and below normal precipitation is dominant in the southern part of the country (during El Niño conditions). Meanwhile, a national climatic picture of wetter conditions is observed when standardised versions of the dry (Nov-Apr) season of the regional precipitation averages are correlated with the ENSO indices
