The consequences of treatment interruptions have been investigated in various patient populations. For patients with controlled viraemia, treatment interruption allowing viral rebound may boost HIV-1-specific immunity. The hypothesis that this will be sufficient to control HIV replication in the absence of treatment has received support in studies of patients initiating treatment during primary infections. In patients with chronic infection, treatment interruption has been shown to boost HIV-1-specific immunity in some cases. In patients with virological failure, despite drug-resistant virus, treatment appears to provide benefit, in that interruption results in a decrease in the CD4 cell count and increases in plasma HIV-1-RNA levels. The removal of drug pressure allows the rapid shift to wild-type virus. Whether this will be of benefit to the patient is not clear. Treatment interruption may help reduce the accumulation of long-term toxicities.