Jacobsen syndrome (JS) is a contiguous gene syndrome resulting from a deletion of chromosome 11q, with various clinical manifestations. A post-term small for gestational age infant was born by normal vaginal delivery without trauma or vacuum extraction. On day 5, right parietotemporal scalp swelling developed, with petechiae on the right cheek and thrombocytopenia (platelets: 63,000/µL). A prominent forehead, wide-set eyes, short and upturned nose were noted. Karyotyping and microarray analysis demonstrated del(11)(q24q25), consistent with Jacobsen syndrome. Brain magnetic resonance imaging (MRI) revealed a huge cephalhematoma. The patient is scheduled to receive periodic evaluations for thrombocytopenia and heart, kidney, abdominal malformations, ophthalmologic and auditory problems. There are lots of newborns with cephalhematoma or petechiae after birth. Not all newborns with these symptoms need evaluations, but if they have these symptoms with suspect features or appearances, we need to go through further evaluations.