The biological characteristics of HIV-1 primary isolates of different recombinant forms (RFs) and non-B subtypes from Galicia, Spain, were investigated and the relationships between biological phenotype and evolution of infection were determined. Peripheral blood mononuclear cells (PBMCs) were obtained during the follow-up of 32 patients infected with HIV-1 non-subtype B genetic forms, characterized in partial sequences of pol (protease-reverse transcriptase) and env V3 region: 12 (37.5%) circulating RFs (CRFs), 9 (28.1%) unique RFs (URFs), and 11(34.4%) non-B subtypes. Primary isolates were obtained by coculture with donor PBMCs. Syncytium-inducing (SI) phenotype was examined in MT2 cell line and coreceptor use in GHOST and U87.CD4 cells. Fifty percent of tissue culture infective dose (TCID50) and viral phenotype based on V3 net charge and Geno2phenocoreceptor bioinformatic method were determined. Fifty-four HIV-1 primary isolates were obtained. CRF14_BG and BG URFs represented the largest group, being all SI/X4, independently of the CD4+ cell count, viral load, or the duration of infection. By contrast, 10 of 11 CRF02_AG viruses were NSI/R5. The prediction of co-receptor use was concordant with biological characterization in all NSI/R5 and in 23 of 26 SI/X4 isolates. The presence of SI/X4 or SI/X4,R5 isolates at early stages of the infection in addition to a decrease in CD4+ counts below 500 cells/µl between 2 and 6 years since diagnosis was observed in all patients infected with CRF14_BG and BG URFs. These data contrast with the usual progression in B subtype infections, in which SI/X4 viruses rarely predominate in the early years of HIV-1 infection. J. Med. Virol. 78:1520–1528, 2006. © 2006 Wiley-Liss, Inc.