To establish the cost-effectiveness of the SQ® grass SLIT-tablet for the treatment of allergic rhinitis including endpoints showing reduction of comorbid asthma symptoms and medication use in a paediatric population using data from a five-year clinical trial (EudraCT: 2009-011235-12). The cost-effectiveness analysis included two treatment arms: the SQ® grass SLIT-tablet plus symptom relieving medication and symptom relieving medication only. A Markov model including four health states was developed: mild AR; moderate to severe AR; mild AR and comorbid asthma; and moderate to severe AR and comorbid asthma. The cost-effectiveness analysis took a German payer perspective. Cost data from a German insurance database analysis and relevant clinical outcomes (i.e. asthma symptoms and medication use, and allergic rhinitis severity) were included in the analysis. The cycle length was one year, discount rates were 3% for both cost and quality-adjusted life years (QALYs), and the time horizon was 10 years. Deterministic and probabilistic sensitivity analyses were undertaken to assess the uncertainty of the cost-effectiveness results. The SQ® grass SLIT-tablet arm resulted in an additional cost of €665 and an increase in QALYs of 0.12. The base-case analysis showed an incremental cost-effectiveness ratio of €5,914, and demonstrated that the SQ® grass SLIT-tablet was cost-effective compared to symptom relieving medication using a cost-effectiveness threshold of €30,000. These results were supported by the probabilistic sensitivity analysis that showed a 90% probability of cost-effectiveness in favour of the SQ® grass SLIT-tablet. Deterministic sensitivity analyses showed that the results were most sensitive to the costs associated with the health state for moderate to severe AR. Based on this analysis, the SQ® grass SLIT-tablet is a cost-effective intervention for allergic rhinitis and comorbid asthma in a paediatric population and can help to relieve the burden of these conditions in a German population.