BACKGROUND AND OBJECTIVE: As available data on HIV-1 strains from Romania indicate the prevalence of a particular subtype- F, not found in other European countries, we aimed at investigating the impact on drug susceptibility of mutations associated with drug resistance and their correlation with the virological and immune response to therapy. METHODS: 38 long term survivors, HIV-1 parenterally infected in childhood, with repeated virological failures, were genotyped for drug resistance and subtype determination. A phylogenetic tree of aligned reversetranscriptase sequences was built. RESULTS: 94.7% of all the patients'strains were subtype F1, clustering together with other Romanian and Angolan F1 strains. Despite the long and complex treatments, 15.8% of patients had wild type virus, 68.4% were fully susceptible to protease inhibitors, 47.3% to non-nucleoside reverstranscriptase inhibitors, 28.9% to nucleoside reverstranscriptase inhibitors. Only 13.2% were resistant to all antiretroviral drug classes. A significantly higher total number of mutations were encountered in severely immunosuppressed patients, who presented also major mutations in the protease gene (V82A, I54V, G48V) and the major M184V mutation associated with type 2 thymidine analogs mutations in reverstranscriptase gene. CONCLUSION: A good immune status seems to be associated with a low range of mutations, indicating the impact of immune restoration or preservation on the therapeutic success rate. The slower post-HAART progression of mutational pattern of HIV- 1 subtype F1 in long term survivors may also influence the viral replicative fitness, a fact that can explain its steady prevalence in Romania.