FastME is a distance based phylogeny reconstruction algorithm. FastME showed better topological accuracy than NJ, BIONJ, WEIGHBOR and FITCH, in all evolutionary conditions we tested, which include large range deviations from molecular clock and substitution rates. When the number of taxa is high, its superiority over NJ, BIONJ and WEIGHBOR becomes important, while FITCH remains close to FastME but becomes hard to use due to its slowness. FastME is very fast, even faster than NJ, and can easily be applied to very large data sets (> 1000 taxa).