An acute clinical picture of variable intensity may occur during the Initial primary phase of HIV infection, it may however pass unnoticed. We report 12 seronegative subjects (11 male homosexuals, 1 female heterosexual, aged 18 to 44 years old), that presented an acute clinical picture preceding seroconversion. All had a sudden beginning, resembling an acute mononucleosis in 10 and with all aseptic meningitis in two. Intensity and duration were variable, lasting a mean of 14 (range 5-44) has an remaining asymptomatic thereafter. Most patients presented a discrete leukopenia with lymphopenia at the expense of CD4 lymphocytes, followed by an absolute lymphocytosis in some, with nit increase in CD8 lymphocytes. All became positive for HIV; circulating HIV antigen was identified in three and IgM anti-HIV antibodies were detected during the symptomatic period by third generation ELISA in other three. It is concluded that the clincal picture of primary HIV infection has identificable clinical serological and immunological features and its recognition has diagnostic and preventives Implications.