Overall scale scores from the National Assessment of Educational Progress (NAEP) indicate that there was only minimal improvement in the mathematics performance of high school students between 1978 and 2004. Using recently released data from the Long-Term Trend (LTT) NAEP, this study describes the content covered on the LTT NAEP and the performance of 17-year-old students on that content. In addition, it demonstrates that although overall gains in performance were small, there were areas within mathematics in which performance improved substantially and others in which students in 2004 did not do as well as their counterparts of the 1970s and 1980s. Specifically, performance on 3 items involving multiplication of whole numbers by fractions deteriorated but performance improved on most tasks involving percents and geometry. Performance was stable on most items assessing algebraic reasoning and logical reasoning and was stable or improved modestly on items assessing estimation, interpretation of tables and graphs, and understanding of integers. (Contains 3 figures, 8 tables, and 9 footnotes.)