The aim of this study was to analyze the demographic, clinical and laboratory characteristics and prognoses of children diagnosed with infectious mononucleosis (IM). The demographic features, referral complaints, clinical and laboratory findings, follow-up, and prognoses of 44 patients diagnosed with IM between January 2000 and June 2006 at the Infectious Diseases Department of Hacettepe University Ihsan Doğramaci Children's Hospital were analyzed retrospectively. The children suspected of IM based on clinical findings and whose diagnoses were proven by serological tests were enrolled in the study. In addition, the patients were divided into four groups -namely, age 0-4, age 5-8, age 9-12 and age 13-16, and the differences among groups were investigated in terms of their clinical and laboratory findings. The patients were aged between 3 months and 16 years. The median age was 4, and 56.8% of patients were below age 5. The male/female ratio was 1.6. No statistically significant variation was observed in the seasonal distribution of patients (p = 0.131). The most common referral complaints were swollen cervical lymph nodes or swollen neck (68.1%), followed by fever (43.1%) and sore throat (25%). Lymphadenopathy (79.5%), tonsillopharyngitis (72.7%), splenomegaly (34%), and hepatomegaly (25%) were the most common physical examination findings. Leukocyte count was normal in 68.3% of the cases. Leukocytosis was detected in 29.5% of the patients, and leukopenia in 2.2%. Lymphocytosis was detected in 44.7% of patients. Downey cell was detected in the peripheral blood smear of 23.6% of patients, and thrombocytopenia in 11.3%. Elevated alanine aminotransferase and aspartate aminotransferase levels were detected in 61.9% and 90.4% of patients who were investigated for these parameters, respectively. The clinical, hematological and biochemical findings of patients did not vary significantly among age groups (p > 0.05). Only one complication (hemophagocytic syndrome) was observed in one patient.