BACKGROUND: Skin prick tests (SPTs) and allergen-specific serum IgE (sIgE) measurements are the main diagnostic tools for confirming atopic sensitization. Results are usually reported as "positive" or "negative", using the same arbitrary cut-offs (SPT>3mm, sIgE>0.35 kUA /L) across different ages and sexes. We investigated the influence of age and sex on the interpretation of allergy test in the context of childhood asthma. METHODS: In a population-based birth cohort (n=1051), we ascertained the information on asthma/wheeze (validated questionnaires), and performed SPTs and sIgE measurement to inhalant allergens (dust mite, cat, dog) at follow-ups between ages three and 11 years. We investigated the association between quantitative sensitisation (sum of SPT mean wheal diameters [MWD] and sIgE titres to the three allergens) and current wheeze and asthma across ages and sexes. RESULTS: We observed a significant association between the SPT MWD and sIgE titres and wheeze/asthma at most ages and for both sexes. However, the strength of this association was age and sex-dependent. For SPTs, the strength of the association between MWD and asthma increased with increasing age; we observed the opposite pattern for sIgE titre. For any given SPT MWD/sIgE titre, boys were significantly more likely to express clinical symptoms, particularly in early life; this difference between males and females diminished with age, and was no longer significant by age 11 years. CONCLUSIONS: Age and sex should be taken into account when interpreting the results of skin tests and sIgE measurement, and age- and sex-specific normative data are needed for these allergy tests. This article is protected by copyright. All rights reserved.