BACKGROUND: The human immunodeficiency virus 1 (HIV-1) infections in Brazil are predominantly caused by two subtypes, B and C. OBJECTIVES: Here we present the characterisation of a novel HIV-1 recombinant form, indicating a new Brazilian CRF_BC, named CRF146_BC. METHODS: RDP, JphMM and Simplot recombination tools were used to evaluate the mosaic pattern. FINDINGS: In this work, we identified three HIV-1 nucleotide sequences previously classified as unique recombinant forms (URFs), plus one new partial genome sharing the same BC recombination pattern. The mosaic genome is almost entirely represented by the subtype C sequence, with a small subtype B recombination region in the pol gene, at the Integrase level. The phylogenetic analyses strongly indicate a common origin between the strains, which were isolated in Rio Grande do Sul, Rio de Janeiro and Bahia states. MAIN CONCLUSIONS: Thus, the new HIV-1 CRF146_BC is circulating in three different Brazilian regions: South, Southeast and Northeast.