The polyomavirus JC (JCV) establishes a persistent infection in the kidneys, and is the virus agent that causes the demyelinating disease progressive multifocal leukoencephalopathy. PCR and DNA sequence analyses of partial JCV genomes have shown that there are at least four main JCV types, each associated with a specific geographical region. Type 1 is of European origin, Type 2 is Asian, Type 3 is found in individuals of African decent and Type 4 is a potential recombinant of Types 1 and 3, and is widely distributed throughout the population of the United States. A comprehensive phylogenetic analysis of 22 complete JCV genomes excluding part of the regulatory region was accomplished using neighbour-joining, UPGMA and maximum parsimony methods. The resulting UPGMA and parsimony phylogenies suggest that the European Type 1 strains diverged from the other types during the evolution of JCV and that each of the other genotypes (and subtypes) falls into well-supported clades. This is the first whole genome approach to phylogeny reconstruction for JCV and represents a significant improvement over earlier studies that were limited to partial JCV sequences and the neighbour-joining method.