Systemic lupus erythematosus has not yet been associated with mutations in the Wiskott-Aldrich syndrome gene; moreover, the time courses of platelet number and size in patients with Wiskott-Aldrich syndrome are unknown. In this case, we present the time trends of platelet count and volume and the histopathology of the kidney of a patient with systemic lupus erythematosus and a mutation in the Wiskott-Aldrich syndrome gene. The patient suffered from congenital recessive X-linked thrombocytopenia, and he developed systemic lupus erythematosus at the age of 12 years. Thus, his disease was reclassified as Wiskott-Aldrich syndrome, class 5. The g.257G > A mutation in the Wiskott-Aldrich syndrome gene and reduced expression of the specific messenger were revealed by molecular analyses. Lupus (2009) 18, 273-277