Cova da Beira is an interior central region of Portugal, with a population of 93,000 inhabitants. The first pollen counts performed in Portugal revealed the highest values of the country in this area. The aim of this study was to assess the aeroallergens sensitization in an allergic population, according to the age groups. In a 5 year period (1995-2000) 1790 consecutive outpatients were observed for suspected allergic symptoms. We included in this study all the 557 paediatric (< or = 15 years old) observed patients (317 male (57%) and 240 female (43%) with an average age of 7.6 < or = 4.2 years old). They were divided in three age groups (Group I: < or = 5 yr; Group II: 6-10 yr; Group III: 11-15 yr). 371 patients were submitted to skin prick tests to aeroallergens. 86.5% of these patients were sensitised to at least one allergen extract. The most representative aeroallergens sensitization were grasses mixture (44.9%), D. pteronyssinus (32.5%), D. farinae (29.1%), Olea europea (27.5%), Parietaria judaica (23.4%), cat dander (16.1%), Artemisia vulgaris (17.6%), Robinia pseudoacacia (12.2%), Platanus acerifolia (11.4%), Tilia cordata (11.4%) moulds mixture (11.2%), Plantago lanceolata (10.6%), dog dander (10.4%), and Pinus radiata (7.5%). The sensitisation to indoor aeroallergens, was similar in all age groups and it was less important than that of pollens. The prevalence of sensitisation to grasses was the greatest in all ages and the house dust mites sensitization was the second most prevalent. The highest pollens counts in this region could explain the early sensitisation even in young children.