New sequences have been produced of the ITS rDNA region of twenty-nine species of Parmeliaceae and analysed by neighbour-joining maximum likelihood distance analysis, and maximum parsimony analysis. Twelve monophyletic groups have been identified, most of which correspond to proposed generic segregated from Parmelia s. lat. Parmelia and Parmelina, Melanelia, and Punctelia appear as independent monophyletic groups; the type species of the two latter genera were, however, not included in the analysis. The parsimony analysis does not support Xanthoparmelia as a monophyletic group separate from Neofuscelia, and Rimelia reticulate is nested within Parmotrema. Parmelinopsis horrescens is more closely related to Hypotrachyna revolute than to Parmelina. Genetic distance values suggest that Flavoparmelia caperata is closer to Parmotrema than to other taxa included, and that Platismatia glauca and Hypogymnia tubulosa are closer to Parmelia s. lat. than to the Physciaceae. However, there is no conclusive support for any of thelatter groupings in the parsimony analysis. We conclude that the ITS region contains valuable information for studying generic delimitations within the family Parmeliaceae, but our study suggests that this region will not conclusively resolve within-family relationships in this group.