Background Approximately one-third of people living with HIV in Ukraine are unaware of their HIV status. Index testing (IT) is an evidence-based HIV testing strategy that supports voluntary notification of partners with HIV risk, so they can receive HIV testing, prevention, and treatment services. Methods Ukraine scaled up IT services in 2019. This observational study of Ukraine’s IT program covered 39 health facilities located in 11 regions with high HIV burden. The study used routine program data from January—December 2020 to describe the profile of named partners and explore index client (IC) and partner factors associated with two outcomes: 1) completing testing; and 2) HIV case finding. Analysis used descriptive statistics and multilevel linear mixed regression models. Results The study included 8,448 named partners, of whom 6,959 had unknown HIV status. Among them,72.2% completed HIV testing and 19.4% of those tested were newly diagnosed with HIV. Two-thirds of all new cases were among partners of ICs who were recently diagnosed and enrolled in care (< 6 months), while one third were among partners of established ICs. In adjusted analysis, partners of ICs with unsuppressed HIV viral load (VL) were less likely to complete HIV testing (adjusted odds ratio [aOR] = 0.11, p < 0.001), but more likely to receive a new HIV diagnosis (aOR = 1.92, p < 0.001). Partners of ICs who cited injection drug use or having a known HIV + partner as their own reason for testing were more likely to receive a new HIV diagnosis (aOR = 1.32, p = 0.04 and aOR = 1.71, p < 0.001 respectively). Involving providers in the partner notification process was associated with completed testing (aOR = 1.76, p = 0.001) and HIV case finding (aOR = 1.64, p < 0.01), compared with notification by ICs. Conclusion HIV case detection was highest among partners of recently diagnosed ICs, but IT participation among established ICs still yielded an important share of all newly-identified HIV cases. Areas for improvement in Ukraine’s IT program include completing testing for partners of ICs with unsuppressed HIV VL, with history of injection drug use or discordant partnerships. Using intensified follow-up for the sub-groups at risk of incomplete testing may be practical. Greater use of provider-assisted notification could also accelerate HIV case finding.