Girls have caught up with boys in math course taking in high school but reasons for taking math still differ by gender. This study, therefore, investigated gender differences in the linkage between peer relations and math course taking by applying multilevel modeling to a nationally representative data set that includes peer networks and school transcripts (N = 6,457 American 9th to 11th graders, aged 13-19). For all adolescents, math course taking was associated with the achievement of their close friends and, to a lesser extent, their coursemates. These associations tended to be stronger toward the end of high school and weaker among adolescents with a prior record of failure in school. Each of these patterns was somewhat more consistent among girls.