The abundance, genomic organization, species distribution, and structure of 33 distinct families of repetitive DNA in Phytophthora are described. The families were identified by screening a library of Phytophthora infestans DNA for repetitive sequences. These was subsequently characterized within 26 species distributed within each of the six taxonomic groups traditionally defined within the genus. Some repeat elements were specific to P. infestans and its close relative, Phytophthora mirabilis, while other repeated sequences were present in most species. The distribution of the DNA families did not conform to the traditional taxonomic groups used for the genus. Characterization of the repeated sequences in P. infestans indicated that they included both dispersed and tandemly repeated elements, with copy numbers ranging from 70 to 8400 per haploid genome. In total, these repeats were estimated to represent 51% of the nuclear genome of P. infestans. Reverse transcriptase motifs were detected in seven of the repeat families that were widely distributed throughout the genus.