OBJECTIVE To determine the viral etiology of severe lower respiratory tract infections (LRTIs), their clinical significance and prognosis among critically ill children. METHODS A prospective descriptive study was carried out. METHODS Pediatric Intensive Care Unit (PICU) of Istanbul Medeniyet University, Goztepe Training and Research Hospital, Istanbul, Turkey. METHODS A total of 115 patients hospitalized in the PICU were evaluated for inclusion in the study. Children with underlying comorbidities and those who did not require mechanical ventilation were excluded. METHODS Demographic, clinical, laboratory test and radiographic data were recorded. RESULTS A total of 63 patients were eligible for the study. The most common diagnosis was bronchiolitis (57.1%). Respiratory syncytial virus (RSV) was the most frequent causal virus (36.5%). The most common complication was acute respiratory distress syndrome (ARDS) (28.6%). Multiple viral infection was identified in 20.6% of the patients, the most common in this subgroup being rhinovirus. Patients with bocavirus infection had a higher likelihood of needing invasive mechanical ventilation (IMV) at presentation. Children who died were likely to be < 12 months old, have ARDS, hepatitis, pneumomediastinum, multiple viral infection, and required IMV support with an increased duration of MV. Additionally, they were found to have a high Pediatric Risk of Mortality III score, Predicted Death Rate and increased need for inotropic support at admission. CONCLUSIONS Our study showed critically ill children with LRTI without known risk factors to have high mortality when aged < 12 months, in the presence of multiple agents and when certain complications (ARDS, hepatitis) and X-ray findings were identified.