A family of transposable elements are described from an oomycete, the plant pathogen Phytophthora infestans, which belong to the hAT group of DNA transposons. The family, named DodoPi, was identified by studying a hotspot of retro- and DNA transposon insertions adjacent to the mating type locus. The DodoPi family contains a small number of full-length copies, which measure 2.7-kb and are predicted to encode a 617 amino acid transposase-like protein, and truncated copies. Both types contain 12-bp terminal inverted repeats flanked by 8-bp target site duplications. Despite the detection of a DodoPi transcript and many polymorphisms between isolates, conclusive evidence of recent transposition was not obtained. A phylogenetic analysis indicates that DodoPi was novel, with only modest similarity to some elements from plants and fungi. Relatives were detected in only some members of the genus. This is the first DNA transposon identified in the stramenopile group of eukaryotes.