AIM: Secondary thrombocytosis occurs commonly in children and is associated with a variety of lower respiratory tract infections, bacterial most often than viral. Aim of the study was to have an insight into the incidence and the clinical significance of thrombocytosis in children with lower respiratory tract infection caused by viral pathogens.METHODS: Clinical data of 92 children, aged 10 days to 8 years, hospitalized with viral lower respiratory tract infection were studied retrospectively for presence of thrombocytosis (platelet count >500×109/l).RESULTS: Thrombocytosis was detected in 59.78% of patients. When children with and without thrombocytosis were compared a significant difference was found for age (P=0.002). We have found no differences among the two groups in sex, SaO2, clinical severity score and CRP levels at admission. Patients with RSV infection presented with significantly higher platelet counts (P=0.003). Extreme thrombocytosis (platelet count >1000×109/L) was noticed in eight patients (8.7%), seven of them were infants with RSV bronchiolitis. All children recovered uneventfully without requiring prophylaxis with anticoagulants or platelet aggregation inhibitors.CONCLUSION: Reactive thrombocytosis is a common finding in the acute care population of children hospitalized with viral lower respiratory tract infection. It represents a reactive phenomenon and does not indicate infection of bacterial cause or severe clinical course. Routine prophylactic antiplatelet treatment or further investigations are not necessary.