Cephalhematomas rarely lead to serious complications such as infection, osteomyelitis and skull fractures. However, we present a newborn infant with hyperkalemia in the context of a serious complication believed to be caused by hemolysis of a large cephalhematoma. The patient was treated with urgent peritoneal dialysis and discharged with a successful outcome. In conclusion, neonates with massive cephalhematoma should be closely examined in terms of bilirubin counts as well as electrolyte counts. (C) 2003 Elsevier Science Inc.