Cancer has been closely associated with human immunodeficiency virus (HIV) infection but this is less frequent in children. Non-Hodgkin's lymphomas represent the most frequently reported single tumor. The authors report seven cases of malignant tumors resulting from the analysis of all (n = 1321) children enrolled in the Italian Register for HIV Infection in Children. Tumors were distributed as follows: non-Hodgkin's B-cell lymphoma (four cases); and Kaposi's sarcoma, hepatoblastoma, acute B-cell lymphoblastic leukemia (one case each). Hepatoblastoma had never been previously reported in HIV-infected children. Also in the current series, non-Hodgkin's B-cell lymphoma is the most frequent single tumor. Five of the seven cancers belonged to the B-cell line. All but one of the seven children have died. Specific chemotherapy was provided in three cases, with some clinical improvement. The treatment of malignancies in HIV-infected children is hampered by increased risk of opportunistic infections often fatal even in children with apparent remission from the tumor.