A high heterogeneity is found in the HIV-1 genome in vivo, not only between individuals, but also within a single individual. Different types of genetic heterogeneity of HIV-1 can be analyzed: the extension and the evolution of the viral quasispecies in blood, the variation between the virus obtained from different body compartment, the differences between isolates from diverse individuals and between HIV-1 subtypes. The virus population during primary HIV-1 infection is generally homogeneous and the intrahost viral evolution is thought to be forced (in absence of antiviral therapy) by the immune system pressure and is generally related to the length of the immunocompetent period. A group of 12 Italian and Swedish well characterized HIV-1 infected long-term nonprogressors (LNTP) have been analyzed for the viral heterogeneity, calculated in the nef gene and in the long terminal repeat (LTR). The intra-sample variations in LTNP were found comparable with those from 8 progressor patients, while a lower inter-individual diversity was observed in the former. In one LTNP the viral evolution during a four-years period was extremely low suggesting that other factors than the host immune pressure may be involved in modulating the intra- and inter-sample HIV-1 diversity.