OBJECTIVES: Migration accelerates population aging in high-outmigration contexts. Older adults who remain in high-outmigration contexts are at higher risk of reduced support networks and increased caregiving burden, but prior work has not quantified how migration influences older adults' kinship structures in such places. This study aims to estimate the kinship structures of older adults living in Puerto Rico and the presence of migrant kin. METHODS: Data come from the United Nations World Population Prospects from 1950 to 2021. We created a two-sex, multistate, time-variant kinship model to estimate how many and what type of family relationships we can expect for older adults in Puerto Rico and the presence of transnational kin. RESULTS: Our models suggest that a 65+ year-old living in Puerto Rico will have, on average, 5.6 close biological family members in 2021: 2.8 adult children and 2.7 siblings. These numbers represent a decline since 2000, when 65+ year-olds had 6.7 such kin. Under 2021 demographic conditions, adults 65 years of age are expected to have 69% of their total female close kin and 71% of daughters residing in the United States. The expected number of transnational living kin is greater for 2021 compared to 2000. DISCUSSION: Models suggest that future generations of older adults in Puerto Rico will have an increased presence of transnational family members. Thus, public health strategies must adapt to address the needs of transnational families in future generations of older adults.