A preterm infant presenting with a congenital cardiac malformation and thrombocytopenia was found to have a karyotype showing a terminal deletion of the long arm of chromosome 11 of the segment 11q24.1-11qter consistent with Jacobsen syndrome. The infant was later diagnosed with Paris-Trousseau syndrome, commonly associated with Jacobsen syndrome. Because children with cardiac malformations often require high-risk surgical procedures in the early neonatal period, those with platelet dysfunction require prompt identification at birth.