Questions exist regarding the appropriate age for referral of an atopic child to an allergist for environmental skin prick testing. This study evaluates age-specific prevalence of sensitization to aeroallergens from infancy through adolescence. A total of 1394 patients were skin tested, with 57.2% being sensitized to at least 1 aeroallergen. In children younger than 2, the authors found that 26.5% were sensitized, including to dogs (15.5%) and cats (9.2%). Additionally, tree sensitization was demonstrated in the youngest age group (7.8% at 0-2 years; 17.1% at 2-4 years), including in 3 infants less than 1 year old. Sensitization rates to dust mites and trees were the highest in all ages above 4 years, with a peak tree sensitization of 56.4% at 10 to 12 years and a peak dust mite sensitization of 56.8% in the >12 group. Overall, the authors observed increasing sensitization rates throughout childhood for indoor and outdoor aeroallergens (P < .001). Aeroallergen sensitization begins at a young age and increases during childhood.