Rare diseases affect small, dispersed populations and are often studied through multisite designs in which equity-relevant demographic data are essential for inclusive recruitment and accurate interpretation. This study examined how sociodemographic variables are collected and reported in rare disease research and evaluated their alignment with the PROGRESS-Plus framework, which outlines Place of residence, Race/ethnicity/culture/language, Occupation, Gender/sex, Religion, Education, Socioeconomic status, social capital, and additional “Plus” factors, such as age and disability status.