Neuroblastoma is a common tumor in childhood and exhibits heterogeneity and malignant progression. MYCN expression and amplification profiles are frequently correlated with the efficacy of therapy. Arsenic trioxide and imatinib mesylate (STI-571) have been suggested as promising therapeutic agents for neuroblastoma, which has been shown to be resistant to conventional therapy. In order to ascertain whether the combination of arsenic trioxide and STI-571 exerts a synergistic cytotoxic effect on neuroblastoma cells in relation to MYCN status, we evaluated cellular proliferation after 72 h of exposure to arsenic trioxide and STI-571 with or without siRNA against MYCN in SH-SY5Y, SK-N-SH and SK-N-BE(2) neuroblastoma cells. Arsenic trioxide and STI-571 demonstrated a synergistic inhibitory effect on cellular proliferation, while MYCN knockdown had an antagonistic effect on this combined treatment. These results indicate that STI-571 treatment may prove effective for MYCN-expressing or MYCN-amplified neuroblastoma. Furthermore, siRNA therapy targeted to MYCN should be avoided in combination with STI-571 treatment in cases of neuroblastoma.