Although online distance education provides adult learners with an opportunity for life-long learning, there are still factors challenging them to engage in educational processes. The purpose of this study is to explore the challenges faced by adult learners in online distance education through the analysis of the relevant literature. The articles (N=36) published in the key journals in the fields of open and distance education, instructional technology, and adult education were reviewed and analyzed through constant comparative analysis in the current study. The findings reveal that adult learners have challenges related to internal, external, and program-related factors indicating the interrelated nature of these challenges. The findings also show that the challenges experienced by adult learners vary depending on their age, gender, knowledge and skills as well as the context in which they study. The findings of this study, which has an exploratory nature, have several implications for distance education stakeholders such as administrators, instructors, instructional designers, and policy makers.