A new reduction of the astrometric data as produced by the Hipparcos mission was published in 2007, claiming accuracies for nearly all stars brighter than magnitude Hp = 8 to be better, by up to a factor 4, than in the original catalogue. This catalogue is known as the Hipparcos-2 catalogue.
The catalogue is described in "Validation of the new Hipparcos reduction", F. van Leeuwen, A&A, 474, 653-664, (2007).
Details of the data reduction, catalogue construction and verification of the results can be found in Hipparcos, the New Reduction of the Raw Data.
The data is available from CDS in VizieR.