Data on the economic burden of lower respiratory tract infections (LRTI) in young children are lacking in Germany. The objective of the cost-of-illness study was to estimate the economic impact of community-acquired LRTI and nosocomial LRTI as well as of infections due to respiratory syncytial virus (RSV), parainfluenza viruses (PIV) and influ-enza viruses (IV). The economic analysis is part of the PRI.DE study, a prospective, multi-centre, population-b-ased epidemiological study on the impact of LRTI in children aged 0 to 36 months in Germany. The analysis includes children with community-acquired infections (1329 cases treated as outpatients, 2039 cases treated as inpatients) and nosocomial infections (90 cases). Medical ser-vices consumed were generated by chart abstraction and parental expenses data by telephone interviews within four weeks after physician visit or hospitalisation. Costs were evaluated from following perspectives: third party payer, parent and society. Total costs for outpatient treatment are 123 per LRTI case. Stratified by virus type, total costs per case are 163 (RSV), 100 (PIV) and 223 (IV). Total costs per hospitalised LRTI case amount to 2579. Stratified by virus type, total costs per case are 2772 (RSV), 2374 (PIV) and 2597 (IV). Total costs per nosocomial case are 2814. Economic burden due to LRTI is 213 million annually. It is concluded that treatment of LRTI in children up to age three causes a considerable economic burden in Germany. Presented results are the first data describing the economic burden of LRTI in young children assessed by means of the incidence data for Germany. This cost-of-illness study provides basic data for fur-ther decision-making, focusing on the economic assessment of preventive strategies for RSV, PIV and IV infections. Data on the economic burden of lower respiratory tract infections (LRTI) in young children are lacking in Germany. The objective of the cost-of-illness study was to estimate the economic impact of community-acquired LRTI and nosocomial LRTI as well as of as infections due to respiratory syncytial virus (RSV), parainfluenza viruses (PIV) and influ-enza viruses (IV). The economic analysis is part of the PRI. DE study, a prospective, multi-center, population-b-ased epidemiological study on the impact of LRTI in children aged 0 to 36 months in Germany. The analysis includes children with community-acquired infections (1329 cases treated as outpatients, 2039 cases treated as inpatients) and nosocomial infections (90 cases). Medical ser-vices consumed were generated by chart abstraction and parental expenses data by telephone interviews within four weeks after physician visit or hospitalisation. Costs were evaluated from following perspectives: third party payer, parent and society. Total costs Stratified by virus type, total costs per case are 163 (RSV), 100 (PIV) and 223 (IV). Total costs per hospitalized LRTI case amount to 2579. Stratified by virus type, total costs per case are 2772 (RSV), 2374 (PIV) and 2597 (IV). Total costs per nosocomial case are 2814. Economic burden due to LRTI is 213 million annually. It is concluded that treatment of LRTI in children up to three causes a considerable economic burden in Germany. Presented results are the first data describing the economic burden of LRTI in young children assessed by means of the incidence data for Germany. This cost-of-illness studies provides basic data for fur-ther decision-making focusing on the economic assessment of preventive strategies for RSV, PIV and IV infections.