We analysed genomic DNA and mRNA of the p53 gene in a case of myelodysplastic syndrome (MDS) with monosomy of chromosome 17. DNA analysis revealed a mutation at the splice donor site (GT to GC) of intron 5. mRNA analysis revealed the presence of abnormal splicing with 46 nucleotide deletion in exon 5, producing a downstream frame shift and a predicted truncated protein which lacked normal function. The p53 gene mutation at the splice donor site contributes to the inactivation of the p53 gene function and may play an important role in the pathogenesis, progression and therapeutic responsiveness of MDS.