Three Japanese outpatients with human immunodeficiency virus (HIV) infection on anti-retroviral therapy showed evidence of influenza in January 1999. CD4+ T cell counts of these patients prior to the diagnosis of influenza were 72, 248, and 152/mm3, and HIV RNA levels were 19,953, 1,259, and 1,585 copies/ml, respectively. Fever continued 4 to 5 days with no severe complications. One patient showed post-influenzal bronchitis which was effectively treated by antibiotics. None of these patients showed increased serum HIV RNA levels during and after influenza, however, in one patient, a transient reduction of CD4+ and CD8+ cells was seen during the active phase of influenza. Although symptoms of influenza in HIV carriers are generally mild and similar to those in healthy adults, careful follow-up is needed as symptoms of influenza in some HIV-infected patients can be prolonged and serious.