BACKGROUND Several studies have demonstrated that medication is commonly used off-label in children with allergic diseases. The aim of this study was to characterise off-label use of prescriptions for allergic diseases in pre-school children from an allergology outpatient unit. METHODS The clinical files of children aged ≤ 6 years seen in a reference allergology consultation with asthma, allergic rhinitis, and/or atopic eczema were reviewed. A total of 500 patients were consecutively observed from January to June 2012. The data collected included gender, age, diagnosis, and prescriptions with the respective daily dosage. RESULTS A total of 1224 prescriptions were registered. The most prescribed medications were oral antihistamines (34.6%), antileukotrienes (22.6%), topical nasal corticosteroids (20.3%), and inhaled corticosteroids (17.7%). From all prescriptions, 422 (34.5%) were considered off-label for age (62.6%), dosage (31.7%), or clinical indication (5.7%). Off-label use was more frequent in children aged <2 years, with 73.5% prescribed for children of this age. CONCLUSIONS Off-label use of drugs for the treatment of paediatric allergic diseases is high. However, these prescriptions are not necessarily wrong, and are recommended in many guidelines. Randomised controlled studies are limited by methodological difficulties creating the need for more observational studies in order to further evaluate the safety and efficacy of drugs used in children.