Splenic rupture following infectious mononucleosis is rare. The case history is presented of a man who presented with sudden onset pleuritic left chest pain. An ultrasound scan of the abdomen showed an enlarged spleen with an abnormal echo pattern and a CT scan of the abdomen showed severe splenic rupture. The patient remembered that he had been unwell 2 weeks earlier with flu-like symptoms and enlarged cervical lymph nodes. Serological examination was positive for Ebstein-Barr virus, confirming the diagnosis of splenic rupture following splenomegaly due to infectious mononucleosis. Management was initially conservative but he became haemodynamically unstable and an emergency splenectomy was performed.