The purpose of this study was to estimate, at a national level and over time, the participation rates of males and females among those students who formally enrol in American high school music ensembles. Ten cohorts of nationally representative samples of students from 1982 and 2009 were analysed using data from High School Transcript Studies conducted by the National Centre for Education Statistics. Results of the present study indicated that, for the time period studied, females were significantly overrepresented in all three traditional US high school music ensemble areas: choir, band and orchestra. As might be expected, choral music enrolment was the most consistently imbalanced by gender across the cohorts, with roughly 70% female and 30% male enrolment in each of the cohorts under study. The results of this study suggest that the US music education emphasis on ensemble music making promotes gender sorting of females into music at the high school level. This finding raises questions about the dominance of males among the ranks of working instrumental music educators and the efficacy of the profession's attempts to recruit more males into choral singing.