Ataxia-telangiectasia (AT) is a recessive autosomal disorder involving cerebellar degeneration, immune deficiencies, cancer predisposition, chromosomal instability and radiation sensitivity. The majority of AT patients carry truncating mutations (ATM) resulting in prematurely terminated proteins that are highly unstable. To develop a relevant porcine model of AT, we sequenced ATM transcripts, characterized the 5’-untranslated region (5’UTR), identified splice variants and developed constructs for gene targeting. Similar to humans, the porcine ATM gene exhibits extensive alternative splicing. In contrast with humans this involved not only the 5’UTR but also coding regions. Six splice variants with 3 alternative exons were observed in the 5’UTR, three of them spliced out the first coding exon, altering the translation start and giving rise to a putative protein lacking the N-terminus substrate binding domain. Real time PCR analysis revealed variable levels of ATM expression in 24 different tissues. Although each splice variant was ubiquity expressed in all tissues studied, differences in the relative abundances of specific 5’UTRs were detected. The longest splice variant represented at least 60% of transcripts in all tissues. Finally, to knockout the ATM gene by introducing truncation mutation shortly after the start codon, we developed two gene-targeting construct for both known and putative translation start sites, according to splice variants detected. The similarity to humans in extensive alternative splicing of the porcine gene should contribute to a more relevant model for AT than the mouse. (This work was supported in part by USDA/NRI-CSREES grant AG2001-35205-11698, AG2002-35205-12712 and USDA-ARS AG58-5438-2-313 and AT Children’s Project).