Menstruation is a natural, physiological process, but it can be a challenging experience for millions of women around the world. In Nepal, a geographically small yet diverse country of 125 caste/ethnic groups, understanding how caste/ethnicity impacts menstrual health is critical for developing context-specific interventions to improve women's health. A community-based, cross-sectional survey was conducted with 679 women and girls between the ages of 13-51 from the country's most populous castes/ethnic groups. Forty eight percent had high menstrual knowledge, 60% had positive menstrual attitudes, and 59% had positive menstrual practices. Caste/ethnicity was a significant predictor of menstrual knowledge and practices. The caste/ethnic groups Tarai/Madhesi/Other, Newar, Janajati, and Muslim all had statistically significant fewer odds of positive menstrual practices compared to Brahman/Chhetri (high caste groups), with Janajati (indigenous ethnic groups) having the poorest outcomes. Despite Nepal making impressive advances in health, certain caste/ethnic groups have fallen behind in terms of menstrual health outcomes. Consequently, blanket menstrual health programs may not be sufficient for improving menstrual knowledge and practices for all. Future programming should consider the use of local languages and context-specific content that incorporates indigenous beliefs, as well as cultivate partnerships with indigenous health organizations, and develop outcome indicators disaggregated by caste/ethnicity to ensure improved menstrual health for all.