Building on the research of White (2008) and Natcher (2013), who identified a paucity of female representation on co-management boards across the Canadian North, the research reported here set out to understand the implications of this gender imbalance for the experiences of women serving on natural resource co-management boards in the Yukon. Broadly speaking, resource co-management boards include a range of different institutional arrangements in which resource users and government come together to share management responsibilities (Yandle 2003). We explored whether critical mass-defined as a specific number or percentage of women necessary to make their participation within an institution effective-is considered by board members themselves to be a critical factor for the way women participate in co-management deliberations. Through semi-structured interviews with current and former board and staff members, our findings indicate that: 1) a majority of board members feel that the representation of women on co-management boards is necessary to the overall effectiveness of board decision making; and 2) women who served on boards with other female members experienced significantly fewer barriers to their participation than when they were the sole female representative. The intent of this article is to offer a practical application of critical mass theory and, more pragmatically, identify ways in which gender can be accounted for more effectively in co-management processes in Canada.