MicroRNA are endogenous molecules which negatively regulate the expression of a variety of genes. These tiny non coding RNA molecules--18 to 25 nucleotides in length--repress, with efficiency and specificity- translation of target mRNA into protein, according to a process akin to RNA interference. MiRNA are critical in the development of plants and mammals since they play a key role on proteins which regulate the strict spatiotemporal control of each tissue. Very recent reports published during 2005 summer show miRNA as also involved in oncogenesis. Specific miRNA elicit oncogenic and antiapoptotic properties in lymphoma models and glioblastoma, respectively. The expression profile of the two hundred miARN, so far identified, reflects the tumor tissue lineage, leading to a potential tool for diagnosis. The occurrence of miRNA in solid tumors and haematological neoplasia opens new avenues for understanding of oncogenesis and, likely, for management of cancer diseases.