We describe the clinical and biochemical findings in a neonate requiring multiple blood transfusions and phototherapy for alloimmune hemolytic anemia and unconjugated hyperbilirubinemia, respectively. In this newborn, a severe photosensitivity reaction developed and laboratory testing revealed elevated serum and urine porphyrins at the time of the eruption. The cause of the transient porphyrinemia was likely multifactorial. Possible mechanisms include poor hepatic metabolism and reticulocyte hemolysis. However, the exact pathogenesis remains unclear at this time.