The objective of this study was to investigate the long-term impact of low-level viremia (LLV) on all-cause mortality, AIDS and non-AIDS events (NAEs), and virological failure in patients receiving antiretroviral therapy (ART). We analyzed ART-naive adults from the cohort of the Spanish AIDS Research Network (CoRIS) who initiated ART from 2004 to 2015 and achieved plasma viral load (VL) below 50 copies per milliliter. LLV50-199 was defined as 2 consecutive VL between 50 and 199 copies per milliliter, and LLV200-499 as 2 consecutive VL between 50 and 499 copies per milliliter with at least one between 200 and 499 copies per milliliter. Multivariable Cox models were used to estimate the association of LLV with AIDS events/death, non-AIDS events, and virological failure. Of 5986 patients included, 237 (4.0%) experienced LLV50-199 and 168 (2.8%) developed LLV200-499. One hundred seventy-one patients died or developed an AIDS event, 245 had any serious NAE and 280 had virological failure. LLV200-499 was strongly associated with a higher risk of both AIDS events/death [adjusted hazard ratio (aHR), 2.89; 95% confidence interval (CI), 1.41 to 5.92] and virological failure (aHR, 3.25; 95% CI: 1.77 to 5.99), whereas no differences were observed between LLV50-199 and no LLV neither for AIDS events/death (aHR, 1.84; 95% CI: 0.89 to 3.82) nor virological failure (aHR, 1.42; 95% CI: 0.78 to 2.58). LLV was not associated with the occurrence of any serious NAE. In this cohort, LLV200-499 was strongly associated with AIDS events/death and virological failure, but not with any serious NAE. Therefore, vigorous treatment should be implemented in patients with more than 200 copies per milliliter.