The Barbus lacerta species group is reviewed. All species occur in the wider Euphrates and Tigris drainages, the endorheic Lake basins of Namak, Van and Urmia and the southern Caspian Sea basin. Barbus cyri, B. lacerta and B. miliaris are considered valid and one new species is described: Barbus karunensis from the Karun River drainage in Iran. Barbus karunensis is distinguished from the other species in the B. lacerta group by a well-developed middle pad of the lower lip, a short anal fin, a straight posterior anal-fin margin and 59-66+2- 4 scales in the lateral line. We compared COI sequences for a total of 123 individuals from 29 Barbus species to test for mitochondrial monophyly of the B. lacerta species group, including DNA barcodes of 70 individuals from all four species of the B. lacerta group. The estimation of the phylogenetic relationships based on the DNA barcode region places the sequenced Barbus specimens into a largely taxonomical concordant cluster, but also indicates the presence of gene flow among a few species, most likely a consequence of geological events in the past.