A phylogenetic analysis of 15 flatfish species based on 40 morphological characters was conducted to determine the interrelationships of the genera Liopsetta, Pleuronectes and Pseudopleuronectes. The results indicate that Liopsetta forms a monophyletic lineage defined by the reduction of the infraorbital sensory canal of the ocular side, small scale size and small body size. The monophyly of Pseudopleuronectes (including P. obscurus) is supported by the interrupted coronal commissure and of Pleuronectes by the presence of radii surrounding entirely the focus of scales and the absence of scleral bones. The synapomorphies of Pleuronectes and Liopsetta support the hypothesis that these genera are distinct and valid. The relationships of the three species of Liopsetta were incompletely resolved.