The objectives of this study are to describe the incidence of non-B and recombinant HIV-1 strains in newly diagnosed HIV-1 infections in Galicia, northwest of Spain, during a 2-year period (May 2000 to June 2002), and the frequency of resistance-associated mutations in reverse transcriptase (RT) and protease (PR) genes, analysing the polymorphisms more frequently detected in non-B and recombinant viruses. All newly diagnosed HIV-1-infected patients attending the nine public hospitals of the seven main cities of Galicia were included in this study. RT, PR and V3 regions from HIV-1 RNA plasma were amplified and sequenced, being the corrected sequences sent to the Stanford HIV RT and Protease Sequence Database. Nineteen of 85 patients (22.3%) were infected by non-B or recombinant viruses: three subtype C, two G, one F1, one Dpol/A1V3, five CRF02_AG, one CRF14_BG, five BGpol/BV3 and one UKpol/UV3 (U, unknown fragment). Eleven of these 19 patients (57.9%) were foreign individuals living in Galicia infected through heterosexual contact, and the other eight (42.1%) were Spanish intravenous drug users who had shared injection equipment. Five of 85 patients (5.9%), all infected with B subtype viruses, showed resistance-associated mutations in RT (M184V, M41L, L210W, T215Y/D and K219Q). In one patient (1.2%) infected with a subtype G strain, resistance-associated mutations in PR (K20I+M36I+M46I+V82I) were detected. In subtype B viruses resistance mutations in PR were not detected. Several polymorphisms in RT: D123S, Q174K, D177E, T200A, V245Q, and PR: I13V, K20I, M36I, R41K, H69K, L89M were detected more frequently in non-B and recombinants than in B strains (P<0.01 to P<0.001). This study reports a high incidence (22.3%) of newly diagnosed patients infected by different non-B and recombinant HIV-1 strains, in a geographical area of Spain, showing also a high frequency of polymorphisms in RT and PR genes.