<p>This review aimed to examine the barriers to accessing health systems among undocumented migrants in low- and middle-income countries (LMICs). This qualitative review study was conducted to answer the question: ‘What are the tangible and intangible barriers undocumented migrants face in accessing health systems in LMICs?’. Thirty-one studies published in English, Portuguese or Spanish between 2013 and 2023 were included. As a growing body of evidence demonstrates, undocumented migrants are among the most vulnerable populations with access to healthcare services impacted by high costs, legal barriers, document requirements and unclear policy messages. This review found that these barriers are interrelated and complicated by individual and institutional discrimination, xenophobia, and perceptions that undocumented migrants are less deserving and compete for local resources. Delayed care and limited primary healthcare access with critical health consequences were described in all such cases. The review suggests that barriers to healthcare access result from the intersection of outdated legislation, economic factors, weak health systems and service provision, bureaucratic inefficiencies and cultural norms and values. As such, improving access to care for undocumented migrants require intersectoral action and policy change that needs to be guided by context-sensitive research.</p>