Amplification of the MYCN oncogene in neuroblastoma is associated with poor prognosis. The amplified unit of DNA can be up to 1 Mb in size and so could contain additional genes that affect tumour phenotype. Identification of such genes may assist in optimising the determination of prognosis, and could provide new targets for treatment. Three genes have so far been identified, which are frequently co-amplified with MYCN in neuroblastoma, DDX1, NAG and N-cym. In this review, the known or putative properties of the protein products of the genes are discussed, and their possible roles in determining tumour behaviour are assessed.