We have focused our research trajectory on the unmet health needs of public health significance affecting vulnerable populations in the US and Puerto Rico. We conduct health services research related to needs and services for substance use (SUD) and mental health disorders as well HIV, among persons living in prison and in the in the community. Our publications have documented the need for patient-centered services among these vulnerable groups and described the behaviors that place these individuals at risk for preventable adverse outcomes of untreated SUDs within the correctional context. Results of our studies have been used to formulate recommendations to the Puerto Rico Department of Corrections to generate Medication Assisted Treatment expansion for eligible prisoners in the island and have also informed public policy development. In addition, through our participation in multi center studies funded by NIDA, our work has contributed to understand structural factors that need to be considered in the implementation of services for these populations in the criminal justice system in the US. Our current research emphasizes, although is not limited to, the manifestations of stigma towards drug users among health professionals in training and in practice, the internalization of stigma by persons with a SUD and their effects on access, retention, and outcomes of care. In addition, we are studying normative influences on stigma through a qualitative study that examines the representation of drug use, illegal drugs, and treatment for a drug use disorder in printed media in PR from 1950-2012. Studies currently under way will inform stigma reduction interventions among health professionals as well as identify structural factors at the macro-systemic level that contribute to the cultural beliefs about drug users that contribute to the gap in effective treatment options in the island and the US.