OBJECTIVES: To evaluate the cost-of-illness of moderate to severe allergic asthma and/or seasonal allergic rhinitis in Germany from the third-party payers’ and the patients’ perspective. METHODS: Twenty pneumologists and 16 pediatricians (office-based) participated. Five hundred patients (276 children) suffering from moderate to severe asthma and/ or seasonal allergic rhinitis (SAR) were included in this retrospective, cross-sectional cost-of-illness study. Information such as demographic characteristics, consultations, emergency visits, hospitalizations, rehabilitations, out-of-pocket-expenditures such as OTC-medication, copayment or house refurbishment and absence from work was collected with a standardized patient questionnaire. Resource utilization of outpatient care was acquired from 305 patients’ records. Direct and indirect costs were considered. RESULTS: Overall, annual costs per patient rise with increasing severity of allergic asthma and in combination with seasonal allergic rhinitis. The average, annual, per-patient cost for children with SAR is 3071 DEM (€1566), for adolescents, 1509 DEM (€770), and for adults, 2234 DEM (€1139). Annual per-patient costs for severe asthma plus SAR increase to 14.431 DEM (€7360) for children, to 17.059 DEM (€8700) for adolescents, and to 18163 DEM (€9263) for an adult patient. From the third-party payers’ perspective, the main cost drivers are medications, hospitalizations and rehabilitation. Additionally, around 6% of the adults retired early due to asthma or asthma/SAR. From the patients’ perspective, house refurbishment was the most relevant cost factor. For children and adolescents, direct costs are responsible for 60 to 78% of the expenditures, whereas for adults, the indirect costs are responsible for 58% of the expenditures. CONCLUSIONS: The financial burden due to allergic asthma and/or seasonal allergic rhinitis from the thirdparty payers’ perspective is comparable to other chronic diseases such as coronary heart disease (CHD) or diabetes mellitus type 2 in Germany. For patients, their relatives and society, large additional costs accrue.