SummaryAn illness of abrupt onset characterized by mononucleosis-like syndrome, lymphocytic meningitis, generalized erythematous rash, pancytopenia with bone marrow hemophagocytosis, generalized lymphadenopathy and liver dysfunction revealed an acute infection due to HIV. Immunological studies showed cellular immunodeficiency (cutaneous anergia, decreased lymphoproliferative response to mitogens, inversion of the T4/T8 ratio due to expansion of the T8 subset). Histopathology of lymph node showed large germinal centers with atrophic Tcell zones. Seroconversion for HIV occured between the 4th and 5th weeks after onset of disease. CSF examination revealed lymphocytic pleiocytosis and was negative for HIV antibodies. The patient is clinically well after a follow up of 27 months, despite persistence of small lymphadenopathy and discrete immunodeficiency. She remains HIV seropositive and her circulating lymphocytes continue to harbor the virus. HIV should be considered in the differential diagnosis of mononucleosis-like syndrome and lymphocytic meningitis.