Objective Mononucleosis infection (MI) is a generalized lymphoproliferative disorder, mostly caused by Epstein Barr virus (EBV). It usually lasts 2–3 weeks; complications are rare and most serious is spleen rupture.

Aim The aim was to analyze frequency and characteristics of complication in hospitalized patients with EBV MI.

Matherial In this prospective study from 2007 we analyzed 60 hospitalized patients aged between 3 and 18 and divided them into two age groups to better analyze complications; a preschool (age <7) (20 patients) and school age group (40 patients). All patients satisfied criteria of acute MI: positive IgM and IgG antibody against EBV VCA (Viral capsid antigen). We used clinical examination, standard laboratory tests and additional analyses.

Results All patients had fever, sore throat and lymphadenopathy, almost all had splenomegaly. Most frequent complication was second bacterial throat infection (30% in both groups), caused by GABHS (group A beta hemolytic streptococcus), with higher prevalence in the first group, mild thrombocytopenia (2 cases) and upper airway obstruction (1 case) were frequent in the first age group. We had one case with peritonsillar abscess in the second age group. Other complications (pneumonia and anemia) were not age related.

Conclusion The average time of hospitalization was 10 days. All patients completely recovered. We treated them with standard, symptomatic and additional therapy, when necessary (corticosteroids, antibiotics, incision in patients with peritonsillar abscess).