Sun exposure in childhood is the main risk determinant for skin cancer in adulthood. Several questionnaires have been used to examine behaviour patterns in terms of sun exposure in childhood, but none have been subjected to a rigorous analysis of their measurement properties. To evaluate the psychometric properties of a questionnaire adapted to investigate children's sun exposure behaviour, a two-stage validation study was carried out. First, in a transverse study, the questionnaire was administered to a sample of 333 children recruited from schools, and the validity and internal consistency were analysed. Second, 32 children recruited in a hospital setting were interviewed for the test-retest analysis. All the items in the 'Photoprotection habits' category were significantly correlated. Principal components analysis showed that two components accounted for over 53% of the variance. The Cronbach's α-coefficient was 0.63 for the first component and 0.43 for the second. In the stability analysis, the percentage of absolute agreement exceeded 70% for all the questions. The Questionnaire on Habits RElated to Sun exposure during Infancy (CHRESI) questionnaire examines sun protection habits by children. Its proven reliability, validity and stability make it a useful tool both in epidemiologic research and in the development and evaluation of campaigns to reduce the risk of skin cancer.