In this issue of the Quarterly Bulletin and the accompanying supplement, the South African Reserve Bank in cooperation with Statistics South Africa presents revised estimates of the national accounts of South Africa for the period 1946 to 1998. Comprehensive revisions had to be made to the national accounts in order to incorporate new data that have become available, to reclassify certain transactions and to rebase estimates at constant prices. This is the sixth time that revisions of this kind have been made in South Africa. The current comprehensive revision updates and extends the national accounts estimates for the years 1946 to 1998 as published in a supplement to the Quarterly Bulletin of June 1994.In addition to these changes, the current revisions also incorporate the relevant recommendations made in the new international System of National Accounts 1993 (1993 SNA) which was published in 1993. Ongoing economic developments have led to the need for new methodologies to improve economic measurement in changing circumstances. The outcome has been the 1993 SNA, which replaces the 1968 version of the System of National Accounts published by the United Nations. Although it was not possible to accommodate all the recommendations and new principles of the 1993 SNA, the introduction of the 1993 SNA will at least ensure that South Africa’s national accounts are, as far as possible, in keeping with commonly used international standards. In comprehensive revisions the following kinds of changes are usually made:- Definitional and classificational changes, which update the accounts in order to keep pace with developments in the South African economy and international best practices;- statistical changes, which reflect a shift in the base period for the calculation of constant-price estimates and the associated price indices, revised sources of data and improved estimating procedures; and- the redesigning of tables to include or omit series that reflect definitional and classificational changes or to make tables more informative. Comprehensive revisions therefore differ from the regular annual national accounts revisions in the scope of the changes being made and the length of the period to which the revisions apply. In the current comprehensive revision, the definitional and classificational changes had to be made mainly because of the implementation of the recommendations of the 1993 SNA. Statistical procedures were adjusted in so far as it was necessary to allow for the incorporation of newly available data sources, methodological changes according to the recommendations of the 1993 SNA and the new as well as revised data contained in familiar and often-used sources of statistical information.The current revisions draw upon information from all the relevant censuses released between 1994 and 1999, the 1995 income and expenditure survey of households and the results of the population census of 1996 (after an upward adjustment of the preliminary results). In some cases the methods of calculation had to be changed in view of problems encountered with the availability and reliability of data sources. New information about unrecorded and informal economic activities has also been included in the revised national accounts statistics.​