The phylogeny of the Dothideomycetes was investigated using nucleotide sequences of SSU and LSU rDNA. 32 new sequences of these regions from 18 species were aligned with five sequences obtained from GenBank, including two representatives of Pezizomycetes used as outgroup. A combined data set of SSU and LSU rDNA was analysed phylogenetically using neighbour-joining and maximum likelihood. The pseudoparaphysate taxa (Pleosporales incl. Melanommatales) form a monophyletic group. A separation of Melanommatales can be rejected using parametric bootstrapping, and this supports previous results obtained from SSU rDNA studies. The aparaphysate Dothideomycetes form a sister-group to the Pleosporales, but with low bootstrap support. Within these species, two well-supported groups can be distinguished, the Dothideales s. str. and the Capnodiales with Myriangiales as sister-groups. The Myriangiales appear paraphyletic, but this has only poor bootstrap support. A monophyly of Dothideales comprising Capnodiales can be rejected with parametric bootstrapping as well as a subdivision of the loculoascomycetes based on form and opening of the ascomata and ascus. The phylogeny of the aparaphysate taxa requires further studies.