Pseudo (or platelet-type)- von Willebrand disease (vWD) is a very rare autosomal dominant bleeding disorder caused by an abnormal hyper-responsiveness of the platelet membrane glycoprotein (GP) Ib/IX complex, the receptor for von Willebrand factor. We found a heterozygous missense mutation in the GPIb alpha gene in a sporadic case with pseudo-vWD: Met (ATG) to Val (GTG) at residue 239. The mutation was not detected in either parent. Investigation of three variable number of tandem repeat loci, D1S80 (MCT118), vWA and D17S5 (YNZ22), confirmed paternity and the de novo origin of the mutation. Furthermore, we have shown by the TaqI polymorphism analysis, which is located downstream of the GPIb alpha gene, that the mutation occurred in the maternal allele. This is the first description of de novo mutation occurred in pseudo-vWD and/or platelet GPIb alpha gene.