Although amplification of the p53-inhibitory MDM2 locus has been identified in rare cases of NBs and abnormal cytoplasmic p53 localisation has been observed by immunohistochemistry in undifferentiated NBs (for review see Borriello et al, 2002), the mechanism of inhibition of p53-dependent apoptosis remains largely unknown. Here, MDM2 is linked to Nijmegen breakage syndrome.