The evolutionary patterns of each genome RNA segment of Crimean-Congo Hemorrhagic Fever virus (CCHFV) were investigated. Nucleotide sequences from 40 CCHFV strains isolated during time period spanning from 1956 to 2003 were tested. It was found that there is not any global molecular clock ticking at the same rate for CCHFV strains; however a local clock is applicable in S RNA segment among strains in the individual clades. African strains seem to evolve faster than strains from other geographic regions. In the comparative study of 18 strains it was found that the evolution rates of S, M and L segments are 0.34 x 10(-4), 1.22 x 10(-4), and 1.01 x 10(-4), respectively. Many discrepancies in clustering were seen, most probably caused by reassortment events, leading in complex patterns of evolution.