Each HLA locus is normally biallelic; however, exceptionally rare cases with more than two alleles at a single locus have been reported.<h4>Case presentation</h4>We describe a 17-year-old male with mixed phenotype acute leukemia (T/myeloid) who was found to carry three alleles at both the HLA-B and HLA-C loci during pre-transplant evaluation. This evidence concerns the gene HLA-C and acute leukemia.