Human T-cell leukaemia/lymphoma virus type 1 (HTLV-1) was the first human retrovirus discovered and there is an estimate of 15-20 million infected worldwide. Endemic areas are Japan, West Africa, Central Africa, South America, the Caribbean, Middle East, Australia and the Pacific Islands. In Guinea-Bissau, adult HTLV-1 prevalence is 2-3%, and higher among HIV-infected patients.Blood samples were collected in a recent HIV/HTLV survey in Bissau, the capital of Guinea-Bissau. Initially, participants were tested for HTLV serologically. The p24 and LTR regions of the proviral genome were then attempted sequenced. Sequences were analysed phylogenetically and compared with reference sequences for HTLV-1.A total of 3% (78/2583) participants were positive on chemiluminesent assay, six additional samples came from another study. Of the 84 seropositive participants we successfully performed sequencing on samples, from 66 participants, 17 were positive for LTR only, one for p24 only and 48 for both. Sequences were in subgroup D of HTLV-1a cosmopolitan, while HTLV-1g was present in one participant.HTLV-1a subgroup D and, to a lesser extent HTLV-1g, is present in Guinea-Bissau and sequences are very similar, especially within households. Presence of HTLV-1g indicates monkey-to-man zoonotic events and at least two circulating HTLV strains in Guinea-Bissau.MG387979-MG388043 for LTR and MG388044-MG388092 for p24.