Evolutionary conserved breakpoints in Old and New World monkeys and their relation to fragile sites observed in Homo sapiens Evolutionary conserved breakpoints (ECBs) in Old World Monkeys (OWMs) and New World Monkeys (NWMs) are localized in particular chromosomal bands and prone to breakage during the phylogeny. Similarly fragile sites (FSs) are specific regions in Homo sapiens (HSA) which can be induced to form gaps or breaks. Notably FSs can be involved in chromosomal rearrangements in cancer owing as targets of carcinogens; also FSs have been positively correlated with breakpoints of constitutional rearrangements in human. Thus a comparative study of the relation of ECBs and FSs is necessary to uncover the common underlying principles of chromosomal alterations in human diseases and evolution. Chromosomal homologies of HSA and OWMs NWMs have previously been studied by chromosome banding and fluorescence in situ hybridization (FISH). However due to limitations in resolution of such techniques in this study I applied for the first time multicolor banding (MCB) probe sets complemented with selected locus specific and heterochromatin specific probes to characterize ECBs in Hylobates lar eight OWMs and four NWMs. Thus numerous new ECBs were characterized for the first time in detail and centromeric positions in several species could be redefined. Also the results showed that the monkey chromosomes homologous to human #3 #7 and #9 presented enhanced rates of ECBs both in OWMs and NWMs. ECBs of NWMs and OWMs could be followed during evolution and aligned with FSs observed in HSA. Most interestingly more than 60% of ECBs co localized with known FSs and ~70% of ECBs corresponded to breakpoints that can be observed in human disorders. For medical field this data is important as FSs now clearly were aligned on molecular level with ECBs. In other words the disease associated chromosomal defects seem at least in parts be due to breakage prone regions of the mammalian genome.