This article describes a case of human immunodeficiency virus type 1 (HIV-1) infection transmission caused by a bloody knife fight in a robbery. The victim was a 69-year-old man who was not infected with HIV-1, and his wife was HIV-antibody negative. A robber, a 42-year-old man, was HIV antibody-positive since December 2005 and had not taken antiretroviral therapy. The BED IgG Capture incidence EIA (BED-CEIA assay) data showed that the specimens from the victim were compatible with a recent seroconversion. Phylogenetic analysis of fragments of pol, encompassing protease and a portion of reverse transcriptase, and of env genes isolated from the victim, the robber, and a local population samples of HIV-1 positive individuals showed that the victim's HIV-1 sequences were most closely related to and nested within a lineage comprised of the robber's HIV-1 sequences. We provide HIV-1 seroconversion data and phylogenetic analysis as evidence that the HIV-1 transmission likely occurred from contact during the robbery.