Immune thrombocytopenic purpura (ITP) is the most common cause of thrombocytopenia in children and adolescents. However, there are a number of other diagnoses that are often mistaken for ITP. A 10-year retrospective chart review was performed at the Children's Hospital of Alabama to characterize ITP. Initially, 492 patients who had the coded diagnosis of ITP (ICD 287.3) were identified. However, 83 (17%) of patients were found to have alternative diagnoses on chart review. Of the 83 patients, 13 patients (3%) represented coding errors or study classification errors. The 70 remaining patients (14%) had an alternative explanation for their thrombocytopenia, consisting of 31 different diagnoses. The most common diagnoses were familial thrombocytopenia (10%), systemic lupus erythematosus (9%), hypersplenism (9%), neonatal alloimmune thrombocytopenia (7%), Wiskott-Aldrich syndrome (7%), or systemic infection (6%). In total, 16 of the patients (23%) were ultimately diagnosed with one of a number of congenital syndromes with concurrent thrombocytopenia. Although this review confirms that most children with thrombocytopenia are diagnosed with ITP, 14% of the study population manifested other diagnoses. The clinician evaluating a child with thrombocytopenia must keep an open mind about the possible diagnosis and perform a comprehensive and thoughtful evaluation based on the clinical picture. ITP must be a diagnosis of exclusion as misdiagnosis in a child with thrombocytopenia may have a significant impact on morbidity and mortality.