Human neuroblastoma cells often carry non‐random chromosomal abnormalities signalling genetic alterations. Quite frequent are ‘double minutes’ (DMs) and homogeneously staining regions (HSRs), both cytogenetic manifestations of amplified DNA, and chromosome Ip‐deletions indicating loss of genetic information. With the identification of amplifiedMYCNand the demonstration of a consensus deletion spanning the chromosome 1p36.1–2 region it appears now likely that both amplification of a cellular oncogene and loss of a tumour‐suppressor gene play an important role in neuroblastoma. Amplification ofMYCNis an indicator for poor prognosis, even when classical morphological criteria would suggest a better outcome. Consequently, patients with amplification are subjected to more intensive therapeutic regimens. Amplification ofMYCNis a paradigm for the clinical use of an oncogene