Orthorexia nervosa (ON) is an excessive fixation on the consumption of healthy food and an obsession with its biological purity. The aim of this study was to assess the prevalence of ON in a population of Polish urban adolescents and some possible contributory factors.

Validation and adaptation of the ORTO-15 Questionnaire was made in the group of 399 participants (15–21years old). The validation procedure incorporated three basic methods to be applied in the reliability analysis. The reliability analysis of the ORTO-15 Questionnaire based on repeatability of the responses presents a very good (kappa: 0.81–1.00 for 5 items) and a good repeatability (kappa: 0.61–0.80 for 10 items). The reliability analysis based on the value of the Cronbach's α reached a satisfactory level (0.7–0.9). The ORTO-15 questionnaire was considered a reliable tool to identify the risk of ON in population studies in the group of urban youth aged 15–21. Assessment was made among 1899 high school students, 992 girls, and 907 boys, aged 15–21years.

The mean value of the ORTO-15 was 39.2±3.6 points, with no sex difference. The main factors connected with orthorexia, according to the “Orthorexia 35” definition were excess weight, sporting activities, out-of-school activities, smoking status, working parents and a high family income.

This study, of a large number of adolescents, showed a prevalence of ON similar to that recorded in adult populations. This is a first assessment of orthorexia among adolescent population.