In a context of population aging, poverty, and inequalities including in the access to healthcare services, in 2004 Mexico initiated Seguro Popular (SP), a non-contributory health insurance providing coverage for informal sector workers excluded from social security. We analyze the impact of SP on the progression of functional limitations among adults aged over 50 with chronic degenerative diseases previously without stable health insurance. Panel data from the Mexican Health and Aging Study (MHAS) permit a difference-in-difference propensity score matching approach, comparing respondents before (2003) and after (2015) the implementation of SP. Findings suggest that SP affiliation in (or shortly before) 2012 has (weakly) slowed the progression of mobility, IADL, and ADL limitations, with a clearer effect in large urban centers. Reforms in the healthcare sector should address underlying structural barriers, reduce existing inequities, and provide effective access to high-quality services. with increased attention for long-term care needs, to guarantee healthy aging.