A 32-year-old homosexual man was admitted because of acute headache, fever, and lymphoadenopathy. The neurological examination revealed nuchal rigidity and positive Kernig's sign. The cell count of cerebrospinal fluid (CSF) at the time of admission, however, was four per microliter and subsequently increased up to 31 per microliter in three days. The serum antibody for human immunodeficiency virus (HIV) was positive in ELISA and the cell number of CD4 positive population decreased to 280. The RT-PCR for HIV RNA was 7.6 x 10(5) copies per milliliter, which gradually decreased, leading to the diagnosis of meningitis due to HIV itself. The Western blotting for HIV antibodies were positive for p24, p40 and p55, whereas that for gp 41 was negative in serum and CSF, suggesting that the meningitis occurred during the seroconversion in this patient. We surmise that aseptic meningitis during HIV primary infection usually results in mild CSF pleocytosis and sometimes leads to even normocytosis shown as in this patient, probably because cellular immunity is temporally suppressed in acute HIV infection.