Among the many unknowns regarding severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and coronavirus disease 2019 is the way in which sex and gender affect the risk of acquiring the virus, illness presentation, disease management and outcomes. Sex, a biological attribute, and gender, a social construct, may both influence an individual's susceptibility, vulnerability and exposure to infectious disease. 1 Immune function differs between sexes and has been shown to affect an individual's likelihood of acquiring infection upon ex posure, or developing complications. [2][3][4] Indeed, early research has shown that these sex differences in immune response may lead to worse COVID-19 outcomes for males in terms of ability to recover from severe infection. 5 Gender, which comprises roles, norms and behaviours that may vary by sex, is associated with an individual's likelihood of exposure 6,7 (Box 1). Several institutions, including the Canadian Institutes of Health Research, have appealed to researchers to include sex and gender variables in data analysis, to improve the effectiveness of health interventions and promote gender and health equity goals. 8 In previous coronavirus epidemics (severe acute respiratory syndrome and Middle East respiratory syndrome), male sex was associated with worse outcomes; 9,10 similarly, early evidence related to COVID-19 appears to largely show increased mortality among males. 11 However, the prevalence of reported cases varies between men and women by country, suggesting that social, economic and cultural factors may influence either acquisition of SARS-CoV-2 or patterns of testing for suspected infection. We, a consortium of European and Canadian researchers (www.mcgill.ca/going -fwd4gender/), sought to assess the influence of gender-related factors on the relative male-female burden of COVID-19, to further understanding of the risks and impact of the COVID-19 pandemic. How might gender influence observed sex differences in epidemiologic research on COVID-19?Gender-related factors may influence an individual's likelihood of exposure to SARS-CoV-2, but they may also influence whether an individual tries to obtain a test and whether they are given one. These factors are presented in a conceptual framework in Figure 1.Gender identity refers to the way in which individuals identify and express their gender as men, women or gender-diverse. How power, opportunities and resources are distributed among men and women within the political, educational and social institutions of a society reflect the institutionalization of gender. 7 Institutionalized gender norms may directly affect health through differential access to health care, food education and income, according to gender. 7,12-14 Furthermore, they shape social norms that define, reproduce and often justify different opportunities and expectations for women and men, such as social and family roles, job segregation and limitations, dress codes and health practices. Gender roles and norms may be related to sex but are also influen...