Hospitalizations related to the consequences of substance use are rising yet most hospitalized patients with substance use disorder do not receive evidence-based addiction treatment. Opportunities to leverage the hospitalist workforce could close this treatment gap. To describe the development, implementation, and evaluation of a hospitalist-directed addiction consultation service (ACS) to provide in-hospital addiction treatment. Six hundred fifty-bed university hospital in Aurora, Colorado. Hospitalists completed buprenorphine waiver training, participated in a 13-part addiction lecture series, and completed a minimum of 40hours of online addiction training. Hospitalists participated in shadow shifts with an addiction-trained physician. Dedicated addiction social workers developed relationships with local addiction treatment services. Physician-related metrics included education, training, and clinical time spent in addiction practice. Patient and encounter-related metrics included a description of ACS care provision. Eleven hospitalists completed an average of 95hours of addiction-related didactics. Once addiction training was complete, hospitalists spent an average of 30days over 12months staffing a weekday ACS. Between October 2019 and November 2020, the ACS completed 1620 consultations on 1350 unique patients. Alcohol was the most common substance (n = 1279; 79%), followed by tobacco (979; 60.4%), methamphetamines/amphetamines (n = 494; 30.5%), and opioids (n = 400; 24.7%). Naltrexone was the most frequently prescribed medication (n = 350; 21.6%), followed by acamprosate (n = 93; 5.7%), and buprenorphine (n = 77, 4.8%). Trauma was a frequent discharge diagnoses (n = 1564; 96.5%). Leaving prior to treatment completion was commonly noted (n = 120, 7.4%). The ACS completed 47 in-hospital methadone enrollments. The hospitalist-directed ACS is a promising clinical initiative that could be implemented to expand hospital-based addiction treatment. Future research is needed to understand challenges to disseminating this model into other hospital settings, and to evaluate intended and unintended effects of broad implementation.