Over the past years, there is a growing number of newly diagnosed pediatric patients with Crohn's disease (CD). Severe course of CD often requires biological treatment with Infliximab (IFX). Loss of response to biological treatment is a major problem. Mean platelet volume (MPV) was reported as a good marker of sustained response to IFX therapy in adults. This study is to determine whether MPV measured prior to IFX therapy and a er its third dose can be used as a predictive marker of sustained response to biological therapy in children with severe course of CD. 43 pediatric patients with CD who underwent IFX therapy were enrolled into this study. The clinical response was evaluated after the third dose and after one year of IFX treatment (sustained response). The MPV values at baseline and week 14 were compared to the patients with good response to IFX to those with loss of the response. During 52-week IFX therapy, 2 out of 43 patients enrolled in the study did not achieve primary response a er the third dose, another 18 children lost their response to the above therapy a er one year. There was no significant association between baseline and 14th week values of MPV between patients with the sustained response to those with loss of response. In opposite to adult patients, MPV cannot be regarded as predictive factor of sustained response to IFX treatment in pediatric patients.