Monozygotic twin males with an attenuated variant of the Wiskott-Aldrich syndrome (WAS) are described. Diagnostic features included moderate thrombocytopenia with small platelet size and abnormal platelet aggregation responses, chronic eczema, depressed serum IgM and low isoagglutinin titre. Splenectomy was performed on one twin at age seven years who survived a complicating pneumococcal septicaemia ten days after the procedure, but who succumbed to fulminating infection three years later. The importance of recognising the attenuated variants of WAS is discussed.