Partial nucleotide sequences from the 5′ terminus of the nuclear large-subunit (LSU) ribosomal DNA gene (domains C1, C2, D1, and D2) have been determined for ten fucalean species representing eight genera to assess their interfamilial and intergeneric relationships: Ascophyllum nodosum (Linnaeus) Le Jolis, Fucus vesiculosus Linnaeus, Pelvetia canaliculata (Linnaeus) Decaisne et Thuret, Himanthalia elongata (Linnaeus) S.F. Gray, Bifurcaria bifitrcata Ross, Cystoseira humilis Kützing, C. nodicaulis (Withering) M. Roberts, C. tamariscifolia (Hudson) Papenfuss, Halidrys siliquosa (Linnaeus) Lyngbye, and Sargassum muticum (Yendo) Fensholt. Sequences of five other species were used as an outgroup: three from Laminariales [Chorda filum (Linnaeus) Stackhouse, Macrocystis pyrifera (Linnaeus) C. Agardh, and Saccorhiza polyschides (Lightfoot) Batters], one from Sphacelariales [Cladostephus spongiosus (Hudson) C. Agardh,] and one from Cutleriales [Cutleria multifida (Smith) Greville as both its gametophytic and sporophytic (‘Aglaozonia parvula’) phases]. Sequences were analyzed using neighbor-joining (distance) and PAUP (parsimony) methods. Low homoplasy level and suitable divergence in the sequence data, especially within the most divergent domains D1 and D2, provided suitable information for assessing phylogenetic relationships among the fucalean families, genera, and species of Cystoseira. European Fucales appeared as a monophyletic group well supported by high bootstrap proportions. Two robust clades, one corresponding to the families Fucaceae and Himanthaliaceae, and the other to a Cystoseiraceae–Sargassaceae group, were obtained. Fucacean genera were strongly supported as a monophyletic group. Himanthalia elongata of the monotypic Himanthaliaceae, the family status of which is confirmed, appeared as the sister group of Fucaceae. In the Cystoseiraceae–Sargassaceae group, the Sargassum relative position was not well defined vs the robust Halidrys–Bifurcaria–Cystoseira clade. The genus Cystoseira appeared polyphyletic. Within the outgroup, the suspicion that the Laminariales is not monophyletic seems to be confirmed; more surprising was the position of Cutleria, which appeared as the sister taxon of Saccorhiza and needs further investigation.