The aim of the study was to confirm the safety of an orodispersible grass allergen tablet 75,000 SQ-T (Grazax®, ALK-Abelló A/S, Hørsholm, Denmark) in children aged 5–12 yr. The study was randomized, double-blinded and placebo-controlled. Sixty children aged 5–12 yr suffering from grass pollen-induced rhinoconjunctivitis (with or without asthma) from five centres in two countries (three in Germany and two in Spain) participated in the study. They were randomized at the ratio of 3:1 as receiving either Grazax or placebo tablet given sublingually once daily for 28 days outside the grass pollen season. A total of 810 treatment-related adverse events were reported in the Grazax group. The majority of these were local reactions in the mouth or throat and were mostly mild (71%) to moderate (27%) in severity and resolved within days. Thirty-five (78%) subjects treated with Grazax and five (33%) treated with placebo reported at least one treatment-related adverse event. Oral pruritus, throat irritation, mouth oedema and ear pruritus appeared as the most frequently reported treatment-related adverse events. 62% (28 of 45) of the actively treated subjects reported oral pruritus, 36% (16 of 45) throat irritation, 31% (14 of 45) mouth oedema and 22% (10 of 45) ear pruritus. Two actively treated subjects withdrew from the study: one subject due to four adverse events (moderate eye pruritus, moderate pharyngolaryngeal pain, moderate non-cardiac chest pain and moderate dysphagia) and one subject due to a serious adverse event (asthmatic attack). The subjects recovered completely from the events. In conclusion, in the present study, Grazax was in general tolerated in a paediatric population and considered suitable for further clinical investigations in children.