Examining core networks has implications for the ability of first-generation immigrants to build social capital and engage in upward mobility in future generations. Using data from the Greater Boston Social Survey, I examine core networks of Puerto Rican and Dominican immigrants to find determinants of having a non-household centered core network, its size, and racial diversity. Ethnicity, organizational membership, and having medium skin tone all had positive effects on core network size. Puerto Ricans fared better in terms of having a core network as well as racial heterogeneity in their networks. Education was an important determinant of network size and diversity for Dominican immigrants. Overall, organizational membership increased the likelihood of having a more racially diverse core network.