This report focuses on the performance of fourth-and eighth-grade students in Puerto Rico in various mathematics content areas on the 2005 National Assessment of Educational Progress (NAEP) in mathematics. The NAEP mathematics assessment was administered to public school students in Puerto Rico for the first time in 2003. Although NAEP had previously administered some of the assessment in Spanish to students who required accommodations, this was the first time an entire NAEP administration was in a language other than English. The NAEP mathematics assessment was administered again to public school students in both fourth-and eighth-grades in Puerto Rico in 2005. Average scores are presented for all students and for male and female students in Puerto Rico for mathematics overall and for five subscales that represent mathematics content areas. Average scores for public school students in the nation (excluding Puerto Rico) are shown for comparison. In all cases, students in Puerto Rico scored lower than the nation. Numerous sample questions are presented for each content area for each grade, along with response percentages for Puerto Rico and the nation. (Contains 14 figures and 3 tables.)