In this article, the representation of male and female musicians is compared between three major genres of music performance and across three geographical regions: the United Kingdom, Europe, and the United States. Relevant data of artists from 40 world-class orchestras, 40 competition brass bands, and 40 top-selling recorded popular music groups were obtained from the websites of the respective organizations and from other authenticated sources. Information collected included the instruments played by each artist, the artist’s status in the ensemble (e.g., principal/section leader/rank and file player). The membership of each instrumental section was then analyzed for balance of sex representation. Overall, across all three genres, male musicians considerably outnumbered females, but this imbalance was moderated by genre and regional differences. The lowest level of imbalance of sexes was observed in orchestras, with males occupying 60% of orchestral chairs compared with females 40%, but principal chairs/section leaders were found to be predominantly male. In brass bands, males predominated by a ratio of 76% males to 24% females, and section leader chairs were almost invariably occupied by males. In the genre of popular music, male performers massively outnumbered females by 85%–15% in every aspect of performers and group leader roles by 90% to 10%. Possible causes of these imbalances are explored for each genre. In all three genres representation of males and females was found to be closely related to the instruments played, for example, many more females than males were harpists, and many more males were trombonists and tuba players than were females. Reasons for these differences are explored with particular reference to differential patterns of education and musical training and to underlying historical and sociological issues.