The analysis of tumour remains fascinating. While e.g. viruses, methylation of DNA, gene silencing, mutations and deletions have been recognized for some time to play major roles in tumour development, a new player has emerged only recently: microRNA or miRNA. An Open Access review in Current Biology ( http://dx.doi.org/10.1016/j.cub.2014.06.043) features this new class of molecules and describes how they act on tumours. A must read!