Vietnam made progress transitioning from a criminal justice to a health treatment response for substance use disorders (SUD) in recent years. This case study describes the evolution of Vietnam's SUD treatment system from 2005 to 2020 to understand and learn from the phases of its development. The case study is based on data from a predesigned interview guide for 47 respondents, literature and policy desk review and direct experience of the authors. Vietnam saw remarkable growth of opioid use disorder (OUD) treatment from 2005 when methadone was unavailable, to 2020 with 335 methadone clinics in all 63 provinces serving more than 52,200 patients. The growth in OUD treatment accounts for much of Vietnam's success managing its HIV epidemic for which injection drug use was a major vector. An unintended consequence, however, focused only on OUD as a strategy to address HIV and was unable to address multiple substances. Most elements of a modern evidence and community-based SUD treatment system exist in Vietnam; however, they are siloed and influenced by multiple government administrative jurisdictions. Faced with rising amphetamine and persistent alcohol use, the path ahead for Vietnam involves a choice between a reliance on compulsory rehabilitation centers or a plan to broaden the scope of substances and treatments, and further integrate with Vietnam's commune-based primary health system.