Splenic infarction is a common cause of left upper quadrant pain and must be suspected in patients with hematologic or thromboembolic conditions and signs of localized or systemic inflammation. Although several mechanisms have been proposed for splenic infarction in patients with various hematologic disorders, hereditary spherocytosis (HS) is usually not associated with an increased risk for thromboembolic events. We report a 13-year-old male with HS who was referred to our hospital with a 4-day history of fever and left upper quadrant pain. Ultrasound scans and magnetic resonance imaging showed lesions suggestive of splenic infarction. Initially, antibiotic treatment was started because secondary infection was suspected. However, 1 week after admission the patient developed typical clinical signs of acute infectious mononucleosis. Further laboratory work up confirmed the diagnosis of acute Epstein-Barr virus infection and additionally revealed protein C deficiency. This association has not been reported previously and may have contributed to the development of splenic infarction. Since infectious mononucleosis is a common cause for clinical consultations in adolescence, physicians caring for children with hematologic disorders should be particularly aware of those possible complications.