Purpose. To assess the immune response to influenza vaccine in children with solid tumors receiving chemotherapy or under the influence of chemotherapy. Methods. Forty-five children (aged 1-18) with solid tumors on chemotherapy or within 6 months of completion of chemotherapy were included in the study. The children received two doses of intramuscular trivalent split influenza vaccine with 1 month apart in November-December 2003 (children < 4 age 0.25 ml; > 4 age 0.5 ml). Antibody titer was detected in the pre-vaccination and 4-week post-vaccination sera by hemagglutination inhibition (HI) method. Immune responses were measured as protective, geometric mean titers (GMT), and fourfold rises in HI titers. Results. We revealed that the post-vaccination GMT for each of the three antigens in patients with solid tumors has increased significantly (P < 0.05). A fourfold rise in the percentage of post-vaccination antibody titers has been detected as 84.4% for H1N1, 77.8% for H3N2, 60% for B. Stratification of patients as on active chemotherapy or being within 6 months of completion of chemotherapy in terms of fourfold rise in antibody titers exposed a statistically significant difference for only B (P=0.34). Post-vaccination protective rates were between 86 and 97%. Conclusions. Due to the interruptions in treatment caused by influenza infections and economic benefits of the vaccine, we suggest that inactivated influenza vaccine should be applied as two doses annually in patients with solid tumor.