Henoch-Schonlein purpura (HSP) affects predominantly the skin, joints, gastrointestinal tract and kidney. Although the pathogenesis is probably of immune origin and complement activation is thought to play a role, laboratory findings including the serum level of the complement components are usually normal. We present a patient with a severe form of HSP nephritis who had unusual laboratory findings of a low level of C3, mild leukopenia and thrombocytopenia. These findings may further support the importance of complement activation in the pathogenesis of HSP.