Seronegative HIV-1 infection has important implications for diagnosis and prevention. We describe a case of HIV-1 infection without seroconversion and fast progression to AIDS and death.Genetic and phylogenetic analysis indicated that the patient was infected with a CRF14_BG-like strain selectively transmitted by his seropositive sexual partner. The results suggest a massive infection with a highly aggressive CRF14_BG-like strain and/or the presence of an unidentified immunological deficiency that has prevented the formation of HIV-1-specific antibodies.