Henoch-Schönlein purpura (HSP) is the most common systemic vasculitis in children. Gastrointestinal (GI) bleeding is one of the major complications affecting one third of the cases which may cause serious morbidity. Platelet volume directly correlates with the platelet function and activation. Small platelets have lower functional capabilities than larger ones. The aim of this retrospective study was to evaluate levels of mean platelet volume (MPV) in patients with HSP compared with healthy controls and to investigate the relationship between MPV and gastrointestinal bleeding. The study consisted of 43 HSP patients (male/female = 25/18, mean age = 6.2 +/- 2.6 years) and 27 age-matched healthy children (male/female = 14/13, mean age = 6.9 +/- 2 years) as control group. HSP patients had significantly lower MPV levels than healthy controls (7.5 +/- 0.8 vs. 7.9 +/- 0.5, p = 0.027). Thirteen of 43 patients had gastrointestinal bleeding. MPV was significantly lower in patients with GI bleeding than patients without bleeding (7.0 +/- 0.8 vs. 7.7 +/- 0.6, p = 0.01). Platelet counts, white blood cell counts, and C-reactive protein levels were significantly higher in patients with GI bleeding when compared to patients without GI bleeding (p = 0.03, p = 0.004, and p = 0.03, respectively). This study suggests that low MPV may contribute to GI bleeding in HSP.