The aims of this retrospective study were to assess the prevalence of primary genotypic resistance to antiretroviral drugs in untreated HIV patients in Spain using the line probe assay and to determine its possible relationship to several epidemiological variables. The global prevalence of primary resistance was 12.5%. Primary mutations in the reverse transcriptase gene were found in two (2.2%) samples: M41L, K70R and M184 V were found in one sample and K70R in another. Primary mutations in the protease gene were detected in 12% of cases; V82A was the mutation most frequently detected (11/12, 91.6%). No statistical significance was found for any of the epidemiological variables studied. In conclusion, the prevalence of primary resistance detected is similar to that found by other authors.