Background Young men involved in the criminal justice system face disproportionately high rates of sexual risk behavior, drug, use, and violence. Little is known about how their involvement in sex partnerships might mitigate their unique health and social risks. This study explores whether sex partner experience protects against harmful sexual behaviors, drug problems, violence, and recidivism in 16-18-year-old Black and Latino men leaving a US jail. Methods Data were drawn from the Returning Educated African-American and Latino Men to Enriched Neighborhoods (REAL MEN) study conducted between 2003-2007, which tracked 552 adolescents during their time in a New York City jail and 397 of them one year after their release. Logistic regression was used to examine the relationship between sex partner experience and sex behavior, drug use, violence, and recidivism. Results This study indicates that young men who have long-term sex partners prior to incarceration are less likely to be inconsistent condom users (OR = 0.50, p ≤ 0.01), have sex while high on drugs/alcohol (OR = 0.14, p ≤ 0.001), use marijuana daily (OR = 0.45, p ≤ 0.001), and carry weapons during illegal activity (OR = 0.58, p ≤ 0.05), especially compared with peers who simultaneously are involved with long-term and casual "short-term" sex partners. However, the positive effects of having a long-term sex partner generally do not apply over time - in this case, one year after being released from jail. Aside from sexual partners, factors such as employment and housing stability predict whether these young men will experience positive or negative outcomes post-incarceration. Conclusions This study highlights the importance and potential benefits of health interventions that engage young Black and Latino men who are involved in the criminal justice system in the US, as well as their sex partners, in health promotion programs. The study also confirms the need for programs that address the employment and housing needs of young men after they leave correctional facilities.