In this paper we report some results of the analysis of released items of the Third International Mathematics and Science Study (TIMSS). This analysis is part of a research project in process related to Mexican high school curricula from an international perspective and, the mathematics students' performance in this school level. The results obtained up to now are related to the mathematical curriculum content underlying the set of TIMSS assessment items. The findings suggest a great wealth of mathematical contents and some skills and abilities needful of answering to this set of items. However, in this paper we report only the results corresponding to mathematical content, highlighting some detected differences between the Mexican high school curricula and these contents. (Author)