Edema of the right thigh; Swollen right thigh; Skin over the swollen right thigh had ecchymosis/ ecchymosis of left hand and forearm; Skin over the swollen right thigh had ecchymosis and discoloration; This case was reported in a literature article and described the occurrence of edema thigh in a 2-day-old male patient who received Hepatitis B vaccine for prophylaxis.   Co-suspect products included hepatitis B immunoglobulin for prophylaxis and vitamin k1 for prophylaxis.   The patient's past medical history included hepatitis b carrier (Family History) (the patient's mother was a hepatitis B virus carrier). Concurrent medical conditions included hemophilia a (factor viii).   On an unknown date, the patient received Hepatitis B vaccine (intramuscular) .5 ml, hepatitis B immunoglobulin (intramuscular) .5 ml at an unknown frequency and vitamin k1 (intramuscular) .1 ml at an unknown frequency. On an unknown date, 36 hrs after receiving Hepatitis B vaccine, the patient experienced edema thigh (serious criteria hospitalization), swelling of legs (serious criteria hospitalization), ecchymosis (serious criteria hospitalization) and skin discoloration (serious criteria hospitalization). The patient was treated with antibiotics nos and intravenous fluid (nos). The action taken with vitamin k1 was unknown. On an unknown date, the outcome of the edema thigh, swelling of legs and ecchymosis were recovered/resolved and the outcome of the skin discoloration was unknown.   The reporter considered the edema thigh, swelling of legs, ecchymosis and skin discoloration to be related to Hepatitis B vaccine.     GSK Receipt Date: 31-Mar-2022 Author Comment: The patient was born at 38 weeks of gestation without complications. There was no abnormality noted at birth. There was no family history of genetic diseases, and prenatal history was unremarkable. Soon after birth, the patient received hepatitis B vaccine and vitamin K1 in right thigh and immunoglobulin in left thigh intramuscularly. The swelling of the right thigh was apparent at about 36 hours after the intramuscular injections. The patient was brought to the baby nursery with edema of the right thigh. On physical examination, the patient appeared well and interactive. He was normocephalic, with normally set ears and without dysmorphic facial features. His lungs were clear to auscultation, with symmetric chest wall expansion. A cardiovascular examination revealed a normal heart rate, with regular rhythm and without murmurs. His abdomen was soft, nontender, and non distended. There was no organomegaly. He had normal genitalia for his age and sex. He had normal range of motion, with normal strength and no head lag. He responded to stimulation, had a symmetric moro reflex, positive suck reflex, and positive palmar grasp reflex. The skin over the swollen right thigh had ecchymosis and discoloration. The infant was transferred to the neonatal intensive care unit (NICU) nursery. A blood culture was obtained, and antibiotics were initiated. Peripheral intravenous (IV) fluid was infused on the left forearm and hand. On the day after NICU admission (day 3 of the patient's life), ecchymosis of his left hand and forearm were noted after removal of the IV angiocatheter. The bleeding at the IV site was noted to prolong. Coagulation (ie, activated partial thromboplastintime [aPTT] and prothrombin time) and platelet count studies were obtained. The aPTT was prolonged. Neurosonogram and cranial CT scans were normal. The diagnosis of hemophilia was made after the factor VIII level confirmed the diagnosis. The patient received factor VIII concentrates. The ecchymosis and swelling gradually resolved without any complications. He was discharged home on day 10 of life. Within a few days of discharge, the patient was seen by pediatric hematologist at the clinic, where his parents were counseled about potential problems (eg, heel sticks, vaccinations, intramuscular injection), including those that may relate to major bleeding, such as intracranial hemorrhage (ICH). Hemophilia A is an inherited bleeding disorder caused by deficiency of coagulation factor VIII. The range of ages for first bleed is wide, with some children having severe bleeding at birth and others who do not experience a bleeding episode until age 4 years. At birth, a diagnosis of hemophilia can be made using cord blood or a venous blood sample. The differential diagnosis of hemophilia includes von Willebrand disease, inherited platelet disorders, factor XI deficiency and factor XIII deficiency. Nicolau syndrome, or embolia cutis medicamentosa, is another condition that would be considered in the differential diagnosis as a complication of intramuscular injection in neonates. Additional Supportive Information: This article is not available for regulatory reporting due to copyright restriction.