The currently available spliceosomal intron data were found to be of limited utility as phylogenetic characters for resolving the phylogeny of several clades of fishes. Phylogenetic relationships were inferred from a parsimony analysis of the distribution of introns among representatives of 18 major groups of vertebrates for seven genes. Phylogenetic signal of the spliceosomal intron data was limited to support for the monophyly of the Teleostei. The spliceosomal intron based phylogeny of B. Venkatesh, Y. Ning, and S. Brenner (in the Proceedings of the National Academy of Science, 1999) was evaluated and found to be fundamentally flawed. The analysis of B. Venkatesh, Y. Ning, and S. Brenner (in the Proceedings of the National Academy of Science, 1999) was compromised by errors in the treatment of missing and polymorphic data, the arbitrary exclusion of taxa, the assessment of homology, outgroups and rooting, the ordering and polarization of character states, and a failure to follow the logical implications of multiple equally parsimonious trees.