To assess the impact of syphilis infection on the risk of HIV-RNA elevation in people living with HIV (PLWH) with current HIV-RNA ≤50 copies/mL. The Italian Cohort Naive Antiretrovirals. All PLWH (2009-2020) under antiretroviral treatment with at least 2 consecutive HIV-RNA values ≤50 copies/mL before the date of syphilis diagnosis and at least 1 HIV-RNA determination after the syphilis event were enrolled. A control group of PLWH without syphilis was matched for mode of HIV transmission. Outcomes were defined using the first HIV-RNA measure in the time window ranging between -2 and +6 months of the diagnosis/index date. The primary outcome used a single value >200 copies/mL to define HIV-RNA elevation associated with risk of transmission. The association between syphilis infection and the protocol defined outcome was evaluated using logistic regression analysis. Nine hundred twenty-six PLWH with a syphilis event were enrolled and matched with a random sample of 1370 PLWH without syphilis. Eighteen of the 926 (1.9%) with syphilis had ≥1 HIV-RNA >200 copies/mL in the window vs. 29/1370 (2.1%) of the not exposed (P = 0.77). In the multivariable analysis adjusted for age, year of diagnosis/index date, and clinical site, syphilis infection was not associated with the risk of HIV-RNA >200 copies/mL (adjusted odds ratio 0.81; 95% confidence interval 0.43-1.52, P = 0.508). We did not find any evidence for an association between syphilis infection and viral elevation >200 copies/mL.