Girls have been overlooked or under-considered within the historiography of Na Fianna Éireann, the Irish nationalist youth organisation co-founded by Countess Constance Markievicz in 1909 as an alternative to the Boy Scouts or the Boys’ Brigade. The purpose of this article is to shed light upon these girls and their activities, situating them within the wider context of the gendered nature of uniformed youth groups in the early twentieth century. In so doing, the article highlights the gender inequality at play within the Irish nationalist movement during the era of the Irish Revolution. Adolescent girls formed a controversial and marginal minority within the membership of Na Fianna Éireann in the cities of Belfast and Waterford in the period 1911-18. The involvement of Belfast Fianna girls in such activities as military drill, camping and gun smuggling challenged the gender conventions of the time. Girls also provided support services to Fianna units during the period 1918-22. In both cases, these girls have received little recognition of their contributions or the risks they ran through real or perceived association with what had become an overtly republican youth group designed to mould a new generation of activists in the struggle for Irish independence.