A particularly unhealthy and high-risk group of individuals at the intersection of the criminal justice and public health systems often cycle between arrest, jail, prison, public hospitals, emergency departments, homeless shelters, and similar institutions over time. This population, while relatively small, represents disproportionate public spending and complex, multidimensional needs. The overarching goal of the current study is to gain a deeper understanding of the patterns and dimensions of frequent cross-system involvement, or repeat cycling between the criminal justice and public health systems. Specifically, the overlap of arrest by police and contact with the ED was examined. A secondary goal was to illuminate what factors work together to encourage or differentiate between various patterns of cross-system cycling. Group-based trajectory modeling was used to determine patterns of arrest and ED contact among adults that accessed these systems in Camden, NJ between 2010 and 2014. These groups were then brought together to determine patterns of cross-system involvement with a focus on patterns representative of frequent cycling between arrest and the ED. These joint groups were then described in detail using descriptive and predictive methods. By comparing across different patterns of frequent cycling, it is clear that cross-system involved individual do not represent a homogenous group; nor is mental illness and substance abuse the only factors driving this overlap. The most frequent joint trajectory groups exhibited significantly more ED visits to address injuries including skull-related injuries, chronic physical health conditions, dental and skin issues, anxiety, depression, suicide attempts, substance abuse and co- and multimorbidity measured as chronic conditions experienced with behavioral health concerns and drug/alcohol abuse. Arrests for disorderly, drug and prostitution offenses were also significantly more prevalent among frequent cross-system cyclers when compared to groups with fewer system contacts. Many of these same factors were also more prevalent among a subsample of young adults aged 18 in 2010 with repeat contacts with both systems. These steps, together with qualitative interviews with service providers in the Camden community, illuminated important factors associated with more frequent arrest and ED contact. These are important contributions to criminological research as discussion is often restricted to behavioral health and is less often concerned with physical health, co- and multi-morbidity. This is also among the first research studies to dig deeper into specific diagnoses associated with frequent arrest and frequent cross-system cycling, among adults and young adults. Healthcare provider interviews were able to confirm that certain issues like dental and skin conditions, depression, anxiety and suicide attempts/ideation tend to increase in prevalence as system contacts accumulate. These are factors that could be targeted earlier in the lifecourse in order to reduce cross-system cycling – an important form of concentrated disadvantage and vulnerability on which to focus attention and resources. / Criminal Justice