Pallister-Killian syndrome (PKS) is a rare genetic disorder usually characterized by mosaic tetrasomy of isochromosome 12p detected in cultured fibroblast cells. We describe here a patient with PKS and intrachromosomal triplication of the short arm of chromosome 12. Her karyo-type was mos 46, XX, inv trp(12)(p11.2p13)[34]/46, XX[16]