Background: Despite increasing access to antiretroviral therapy (ART), the proportion of eligible patients initiated on treatment remains suboptimal. Only 64.6% of the people living with HIV (PLHIV) globally were initiated on ART by June 2019. The streamlined ART (START-ART) implementation study was based on the PRECEDE model, which suggests that "predisposing, enabling, and reinforcing" factors are needed to create behavior change. START-ART increased ART initiation within 2 weeks of eligibility by 42%. However, the gains from some implementation interventions erode over time. We evaluated facilitators and barriers to sustainability of this streamlined ART initiation in the year following the implementation period. Methods: We designed a mixed-methods explanatory sequential study to examine the sustainability of START-ART implementation. Quantitative component consisted of cross-sectional patient chart reviews of routinely collected data; qualitative component consisted of key informant interviews of health workers in START-ART facilities 2 years after conclusion of the implementation period. We analyzed data from 15 public health centers of Mbarara district, where the START-ART implementation was carried out.