Activation-induced cytidine deaminase (AID) is involved in immunoglobulin affinity maturation, gene conversion and class switch recombination. This protein is therefore a major actor in the creation of the antibody repertoire. We have isolated, for the first time, the AID mRNA from a urodele amphibian, Pleurodeles waltl. This mRNA encodes 198 amino acids and shares 70% and 76% of similarity with Xenopus laevis and human AID sequences, respectively. All consensus motifs necessary for AID functions are present, suggesting that AID is functional in P. waltl. P. waltl AID is encoded by five exons as in other species. However, in contrast to mammalian AID, no splice variant could be detected in that species. We also noted that AID is predominantly expressed in the spleen, the major secondary lymphoid organ of P. waltl, and that the transcriptional regulation of P. waltl AID is partially different from that found in higher vertebrates. Furthermore, we showed that AID is expressed early during P. waltl embryonic development.