Project Abstract The growing prevalence of opioid use disorders (OUDs) in the community and in Criminal Justice Systems drives increasing rates of overdose mortality, poor health, and high costs. Persons incarcerated in local jails and prisons are particularly susceptible to increased risk of unintentional overdose, re-incarceration, and uncontrolled HIV. Methadone maintenance treatment is effective community treatment for OUD. However, the impact of methadone maintenance offered routinely in a large, high-volume, high-turnover municipal jail setting has not been studied. New York City, with a large jail methadone program, a jail electronic medical record, and a rich collection of regional health surveillance databases, presents a unique opportunity to estimate in-jail methadone treatment and associations with post-release overdose, re-incarceration, HIV control, and costs. This study analyses important opioid-related outcomes among NYC jail inmates admitted to and leaving NYC jails during 2011-2017, and compares individuals who: a) accessed the jail methadone maintenance treatment program and were released from jail on methadone maintenance, or, b) were diagnosed with an opioid use disorder but did not access methadone and were released from jail out- of-treatment (detox-only). Secondary, exploratory analysis will examine outcomes among, c) a smaller sample of buprenorphine maintained individuals. We will test the primary hypotheses that methadone maintenance exposure reduced the risk of fatal and non-fatal overdoses and jail recidivism, improved HIV control (among HIV-positive persons), and improved rates of appropriate health care utilization and lowered costs. This study proposes to link New York City jail electronic medical records with NYC-wide overdose, re-incarceration, HIV/AIDS, and related health and economic outcome data to better define the public health impact of methadone maintenance in NYC jails.