Background: Skin prick test (SPT) of immediate hypersensitivity is a main instrument in the diagnosis of allergy. Aim: To demonstrate the applicability of skin prick test in different age groups. Patients and Methods: We studied children and adolescents with the diagnosis of allergy in the Pediatric Respiratory Laboratory of the Catholic University of Chile, from January 2001 to March 2002. The SPT was performed using a standardized technique. The allergens were applied on the volar surface of the forearm in children older than 4 years of age and in younger children it was applied on their back. For study purposes we separated them into three age groups: GI ­2 years and 11 months, GII from 3 to 4 years and 11 months, GIII 5 years. Results: We studied 408 children, aged between 8 months and 15 years. The SPT was applied to all patients with no adverse effects of any kind. There was a positive reaction in 57.7% of children. The reaction was positive in 37% in G1, 39% in GII and 65% in GIII (p <0.001). The predominant allergens for each group were dust mites (Dermatophagoides pteronissinus and farinae). Conclusions: SPT was useful when used on a selected pediatric population. The frequency of sensitization increased significantly with age. However, more than one third of children between 2 and 4 years of age tested positive to one or more allergen, demonstrating its applicability in this age group (Rev Méd Chile 2005; 133: 195-201)