BACKGROUND: As Rwanda inches closer to the UNAIDS HIV first 95 of knowing one's HIV status by 2030, finding the remaining HIV-positive individuals could be difficult by use of passive methods. Index testing is an approach whereby the exposed contacts of an HIV-positive person are notified and offered an HIV test. We aimed to assess the factors related to the HIV-positive outcome among older people (aged 50 years and above) in Rwanda. METHODS: In Rwanda, adults (aged ≥18 years) on antiretroviral therapy (ART) who reported having had sexual partners with unknown HIV status, and individuals with newly diagnosed HIV, described as index cases, were asked to provide details of their sexual partners and invite them to the health facility for HIV testing through client referral, provider referral, or dual referral. We used logistic regression to model the odds of identifying partners who were HIV-positive or aged 50 years or older through partner notification services and to assess predictive factors related to index case and partner, after adjusting for partner related variables (age group, gender, relationship between index and sexual partner, province of residence, notification used) and index case related variables (type of index case, multiple partnership, had unprotected sex in past 12 months, viral load suppression, age difference between notified sexual partner and index case). Written informed consent was obtained from each participant before inclusion in the study. The Rwanda National Ethics Committee approved the protocol for implementation. FINDINGS: Between October, 2018, and September, 2021, 18 453 index cases were recruited and 31 227 partners were notified and tested, of whom 3156 (10·0%) were aged 50 years and older. Of the partners aged 50 years and older, 877 (27·8%) were female and 2279 (88·1%) were male, and 1638 (51·9%) were notified by index cases who were younger than them. Among partners aged 50 years and older, 6·0% (3156) were HIV-positive, with a higher prevalence in partners notified by newly diagnosed index cases 14·7% (46 of 313). In the multivariable analysis, among partners aged 50 years and older, the adjusted odds ratio was 2·66 (95% CI 1·78-3·98) for female partners compared with male partners, 3·14 (2·08-4·77) for partners of newly HIV-diagnosed index cases compared with those of index cases who were already taking ART, and 1·89 (1·07-3·37) for partners who were 15 years older than the index case compared with partners who were 5 years older or younger. INTERPRETATION: Partners of people with newly diagnosed HIV, older individuals who engaged in sexual relationship with younger individuals, and female partners had an increased risk of being diagnosed with HIV. Index testing successfully identified older people with undiagnosed HIV. FUNDING: None.