DNA helicases are molecular motors that catalyse the unwinding of energetically unstable structures into single strands and have therefore an essential role in nearly all metabolism transactions. Defects in helicase function can result in human syndromes in which predisposition to cancer and genomic instability are common features. So far different helicase genes have been found associated in 8 such disorders. RecQ helicases are a family of conserved enzymes required for maintaining the genome integrity that function as suppressors of inappropriate recombination. Mutations in RecQ4, BLM and WRN give rise to various disorders: Bloom syndrome, Rothmund-Thomson syndrome, and Werner syndrome characterized by genomic instability and increased cancer susceptibility. The DNA helicase BRIP1/BACH1 is involved in double-strand break repair and is defective in Fanconi anemia complementation group J. Mutations in XPD and XPB genes can result in xeroderma pigmentosum, Cockayne syndrome and trichothiodystrophy, three genetic disorders with different clinical features but with association of transcription and NER defects. This review summarizes our current knowledge on the diverse biological functions of these helicases and the molecular basis of the associated diseases.