Circulating biomarkers such as somatic chromosome mutations are novel diagnostic tools to detect cancer noninvasively. We describe focal deletions found in a patient with atypical teratoid rhabdoid tumor, a highly aggressive early childhood pediatric tumor. First, we used magnetic resonance imaging (MRI) and histopathology to study the tumor anatomy. Next, we used whole genome sequencing (Next Gen Sequencing) and Bioinformatics interrogation to discover the presence of 3 focal deletions in tumor tissue and 2 of these 3 focal deletions in patient’s blood also. About 20% of the blood DNA sequencing reads matched the tumor DNA reads at the SMARCB1 gene locus. Circulating, tumor-specific DNA aberrations are a promising biomarker for atypical teratoid rhabdoid tumor patients. The high percentage of tumor DNA detected in blood indicates that either circulating brain tumor cells lyse in the blood or that contents of brain tumor cells traverse a possibly compromised blood-brain barrier in this patient.