The case is described in tomorrow's edition of the Lancet by two Italian doctors, Carlo Gianquinto and Anita de Rossi of the University of Padua.
The boy is living a normal life and appears healthy, although his immune system is reacting as if he still has the infection. The doctors cannot explain how he rid himself of the virus.
They wrote in a letter to the journal: "He has remained free from symptoms. He is now nine years old, his growth and development are normal, and he is attending primary school."
The doctors had first reported on the boy in 1991, when he was four.
His mother, an injecting drug user, was identified as HIV infected when she was eight months pregnant. Because the boy was abandoned at birth, no further information on the mother was available.
The infant did not receive a blood transfusion and was bottle fed. At 16 months, the boy tested negative for HIV and had remained free of the virus ever since.
The doctors said several other children born with HIV had reportedly cleared the infection, but how they did so remained a mystery.
They noticed that the nine-year-old had a declining number of T-cells - a type of white blood cell vital to the immune system. Normally this would be a hallmark of HIV infection. "Although this child remains well, whether children who seem to have cleared the virus are really infected and unable to transmit HIV is an issue that urgently needs to be clarified," the doctors wrote.