Nucleotide sequence data from the Internal Transcribed Spacer 1 (ITS1) in the ribosomal RNA (rRNA) gene cluster were used to determine the utility of molecular data to discriminate species and genera of pseudocerotid turbellarians. We sequenced 388,379 and 415 bp from the ITS1 of Pseudoceros jebborum, Pseudoceros paralaticlavus and Pseudobiceros gratus respectively, to give an aligned sequence for this region of 421 positions. The nucleotide sequence of the ITS1 of Pseudoceros jebborum differed from that of Pseudoceros paralaticlavus by 6% (24/421 positions) and from that of Pseudobiceros gratus by 36% (152/421 positions). These results indicate that sequence data from the ITS1 will be a useful taxonomic tool to discriminate pseudocerotid flatworms.