CD5 has previously been identified in marsupial tissues using anti-human CD5. However, despite the known cross-reactivity of the antibody in marsupial tissues, the cDNA sequence has not previously been characterised in any marsupial. This study has identified the CD5 gene in the opossum genome database and has characterised the CD5 cDNA sequence from the tammar wallaby. Both marsupial CD5 sequences have a high level of sequence identity to known eutherian CD5 sequences, are cysteine-rich and have identical structural motifs to their eutherian homologs. CD5 transcripts were strongly expressed in adult tammar wallaby spleen, mammary node and blood, and expressed at a lower level in liver, kidney and heart tissues. Characterisation of CD5 in marsupials allowed a comparison to the epitope sequence of anti-human CD5 and showed a high level of sequence identity.