This article offers an innovative way of understanding gender balance in parliaments. Motivated by research documenting how newcomers are disadvantaged during their first term in office, while senior members enjoy certain privileges, we want to find out how common women are among senior members of parliaments. We launch an institutional approach comprising three seniority measures to study gender gaps in political endurance to find out whether, where, and when men are more likely than women to be parliamentary seniors. Our analysis using data from seven countries in Western Europe and two countries in North America (1965–2020) shows very high gender gaps across the three measures. Thus, despite an increased level of female representation, women still constitute a small part of the exclusive group of senior members of parliament. Our findings extend the research documenting that women and men largely have equally long parliamentary careers, emphasizing the need to understand gender balance in multidimensional terms.