Subcutaneous fat necrosis of the newborn is a rare form of panniculitis characterized by firm subcutaneous nodules and plaques on the fat pads-rich portion of the body. It usually occurs in full-term infants with associated perinatal problems such as obstetric trauma, hypoxia, meconium aspiration and maternal gestational diabetes mellitus. Although it generally has benign course showing spontaneous regression within a few months, close monitoring is needed until the complete resolution of the lesion as complications could lead to hypocalcemia which is fetal if untreated. A 6-day-old neonate with a history of maternal gestational diabetes mellitus presented with a 3x3 cm sized erythematous to violaceus indurated plaque on back which has lasted for 2 days. He had a mild fever and leukocytosis. Histological examination revealed lobular panniculitis with a infiltration of lymphohistiocytes and radially arranged needle shaped cholesterol clefts in adipocytes. Based on these findings, he was diagnosed with subcutaneous fat necrosis of newborn. We excluded the possibility of sclerema neonatorum because there was no vasculitis. Herein, we report a case of subcutaneous fat necrosis of newborn, which has rarely been reported in the dermatologic literatures in Korea.