The objective of this paper is to evaluate the horizontal inequality of the Spanish Personal Income Tax System between 1982 and 1990, through a se-ries of indices which have been proposed in the recent literature. Furthermore we introduce a new index, developed by Salas (1995), which allows us to evaluate the horizontal inequality as a distributional change and which can be deduced from a social welfare framework. We find that the dif-ferent measures of horizontal inequality show the same temporal evolution. Futhermore, we conclude that the variation of the horizontal inequality seem to be better explained by the composition of family incomes rather than the variation of the Tax System.

Keywords: horizontal inequality, personal income tax, income distribution.