BACKGROUND: Pre-cART (combined antiretroviral therapy) plasma viral load >500,000 copies/ml has been associated with a lower probability of achieving virological suppression, while few data about its role on maintenance of virological suppression are available. In this study we aimed to clarify whether high levels of pre-cART viraemia are associated with virological rebound (VR) after virological suppression. METHODS: HIV-infected individuals who achieved virological suppression after first-line cART were included. VR was defined as the first of two consecutive viraemia >50 copies/ml (VR50) or, in an alternative analysis, >200 copies/ml (VR200). The impact of pre-cART viraemia on the risk of VR was evaluated by survival analyses. RESULTS: Among 5,766 patients included, 59.2%, 31.4%, 5.2% and 4.2% had pre-cART viraemia ≤100,000, 100,001-500,000, 500,001-1,000,000 and >1,000,000 copies/ml, respectively. Patients with pre-cART viraemia levels >1,000,000 copies/ml had the highest probability of VR (>1,000,000; 500,000-1,000,000; 100,000-500,000; 500,000 and >1,000,000 copies/ml showed a significantly higher risk of VR regardless of the VR end point used. No difference in the risk of VR was found between patients with pre-cART viraemia ranging 500,000-1,000,000 copies/ml and those with pre-cART viraemia >1,000,000 copies/ml, regardless of the VR end point used. CONCLUSIONS: Pre-cART plasma viral load levels >500,000 copies/ml can identify fragile patients with poorer chance of maintaining virological control after an initial response. An effort in defining effective treatment strategies is mandatory for these patients that remain difficult to treat.