ObjectiveTo estimate the prevalence of resistance-conferring mutations to antiretroviral drugs in previously untreated patients with chronic HIV-1 infection as a basis for French recommendations on viral genotyping before antiretroviral treatment initiation.DesignResistance mutations were sought in samples from 404 patients seen in 23 specialized centres throughout metropolitan France in 1998.MethodsThe protease and reverse transcriptase (RT) genes of plasma virions were sequenced. Primary and secondary protease and RT gene mutations were identified from the International AIDS Society resistance testing – USA panel.ResultsThe prevalence of patients with primary and secondary mutations were 3.7% (95% CI 1.7–5.7) and 50.3% (95% CI 45.0–55.6), respectively. The prevalence of patients with mutations associated with resistance to nucleoside RT inhibitors (NRTI) and non-nucleoside RT inhibitors was 3.3% (95% CI 1.5–5.1) and 0.8% (95% CI 0.0–1.7), respectively. The prevalence of patients with NRTI primary mutations differed according to whether seropositivity had been diagnosed more or less than one year previously (0.2 versus 2.2%P= 0.023). Primary mutations associated with protease inhibitor resistance occurred at a prevalence of 1.9% (95% CI 0.5–3.4) with no difference according to the duration of known seropositivity.ConclusionIn France, in 1998, the prevalence of patients with primary mutations associated with resistance to antiretroviral drugs was low. Genotyping before the initiation of therapy was not recommended in chronically HIV-1-infected naive patients. A national sentinel survey of resistance in this clinical setting is performed regularly to update the recommendations for resistance testing.