Wiskott-Aldrich syndrome (WAS) is a primary immunodeficiency disorder characterized by recurrent infection, eczema, and microthrombocytopenia. WAS is inherited in an X-linked recessive pattern, and various mutations in the WAS gene on the X chromosome are the genetic basis of WAS. A 7-month-old Korean boy presented with recurrent bloody diarrhea, eczema, and persistent thrombocytopenia with small platelets. Direct sequence analysis of the entire coding region of the WAS gene showed a novel nonsense mutation with a G-to-A substitution at the nucleotide position 756 on exon 8, leading to a premature termination at codon 252 (c.756G>A; p.W252X). Family study revealed that neither of the parents had the mutation, indicating the de novo occurrence of the mutation.