A 13-year-old female patient, with no personal history of interest, consulted for bilateral palpebral oedema of three days' evolution. In the subsequent anamnesis she reported accompanying headache with slight odynophagia, without associated fever. Physical examination revealed bilateral eyelid oedema with no other ocular involvement, no oedema in other locations and tonsillar hypertrophy 2/4 with no exudates. In the following days he consulted again up to three times due to persistent and increased eyelid oedema, with no other symptoms. A urine dipstick was performed on several occasions without detecting proteinuria and a culture of pharyngeal exudate was negative. In view of the clinical findings and the negative results of the tests performed to date, a blood count, blood biochemistry, liver profile and urine sediment were requested, with normal results except for leukocytosis (18,460/µl) with lymphocyte predominance (61.8%) and increased transaminases (GOT 139 IU/l, GPT 184 IU/l). Ten days after the onset of the disease, the eyelid oedema resolved, with no evidence of fever, lymphadenopathy or hepatosplenomegaly. A blood test was performed three weeks later and the haemogram showed no abnormalities and transaminases decreased to normal values (GOT 22 IU/l, GPT 16 IU/l). Suspecting mononucleosis syndrome, serology for EBV and cytomegalovirus (CMV) was requested, obtaining positive IgM against EBV, which allowed the diagnosis to be confirmed.