Clinical manifestations of primary human immunodeficiency virus (HIV) infection (acute retroviral syndrome) and virologic characteristics of HIV-1 have rarely been described in Taiwan. Medical records of patients followed at the National Taiwan University Hospital between June 1994 and September 2003 were retrospectively reviewed to identify HIV-infected patients who were diagnosed with primary HIV infection. Blood specimens obtained at the diagnosis of primary HIV infection were submitted for viral subtyping and genotypic resistance assay. Twenty out of 940 patients were diagnosed with acute retroviral syndrome during the study period. All of the patients were males, with a median age of 31 years (range, 23 to 42 years); all were men who had sex with men. The most common clinical manifestations were fever (95%), generalized lymphadenopathy (75%), pharyngitis (70%), skin rashes (70%), and gastrointestinal symptoms (60%) including nausea, vomiting, and diarrhea. Thrombocytopenia (35%), leukopenia (35%), and elevated liver function test (50%) were seen in the laboratory tests. The median CD4 lymphocyte count was 312 cells/microL (range, 112-520 cells/microL), and the plasma HIV RNA load by reverse transcriptase-polymerase chain reaction was 230,500 copies/mL (range, 602 --> 750,000 copies/mL). No major resistance mutations on protease or reverse transcriptase were identified in the 11 available viral isolates. We conclude that primary HIV infection was rarely diagnosed in the designated hospital for HIV care in Taiwan. More education of health care providers and counseling of persons at risk to increase awareness of HIV infection are urgently needed in Taiwan in order to facilitate earlier diagnosis of primary HIV infection and prevent further transmission.