The purpose of this study is to understand physician treatment decisions in selecting specific second line treatments in pediatric ITP and to determine the effectiveness of different second line ITP treatments. Eligible patients are those ages 1-18 years who are starting on a new second line treatment for ITP, defined as any treatment other than IVIG, steroids, anti-D globulin, or aminocaproic acid. Enrolled patients remain on the study for approximately one year.