In the last decade, microRNAs (miRNAs; small noncoding RNA molecules) as post-transcriptional regulators have been a hotspot in research for their involvement in biological processes and tumour development. However, there have been few reviews focusing on a single miRNA family. The dysregulation of miRNAs appears to play a crucial role in cancer pathogenesis where they exert their effect as oncogenes or as tumour suppressors. This review summarises current studies on the dysregulation of the microRNA-34 (miR-34) family in different types of cancers and its role in the p53 network. The structure of the miR-34 family members includes p53-binding sites reflecting their function as tumour suppressors downstream of the p53 pathway. miR-34 dysregulation occurs in cancers, including several epithelial cancers, melanomas, neuroblastomas, leukemias and sarcomas, in the presence or absence of the p53 mutation. For these cancers, functional restoration of miR-34 is a useful novel therapy. As evidenced from preclinical and clinical studies, the miR-34 family plays an important role in the treatment of miR-34-dysregulated cancers with mutant or wild-type p53. This review will have a potential impact in the clinical treatment of p53-mutant and/or miR-34-dysregulated cancers using a miR-34 restoration approach.