Henoch-Schönlein purpura (HSP) is the most common systemic vasculitis of childhood, but the etiology is not known. Familial occurrence of HSP is rare. There are only two previous reports of the simultaneous onset of HSP in siblings. Herein, we present simultaneous occurrence of HSP in two brothers. Nearly simultaneous onset of symptoms in our cases suggests that a common environmental factor, either infectious or allergic, is possible. Our patients were previously healthy, with no history of atopy. They had neither a history of infection prior to the onset of HSP nor clinical evidence of infection on admission, although antistreptolysin titers were elevated in both patients. The trigger causing HSP was not identified in these patients but we assumed that environmental factors may be responsible for the simultaneous occurrence of HSP in genetically susceptible patients.