BACKGROUND: The alexithymia construct is mainly characterized by a difficulty in identifying and expressing feelings that is thought to reflect a deficit in cognitive processing and regulation of emotional states. During the last decade, alexithymia has been associated with a large variety of medical and psychiatric disorders in the adult population. Although adolescence is probably an opportune time to explore processes of emotion regulation, alexithymia has been rarely examined during this period. The 20-item Toronto alexithymia scale (TAS-20) is the most widely used self-report measure of alexithymia. For this scale, a three-factor structure was proposed: difficulty identifying feelings (DIF), difficulty describing feelings (DDF) and externally oriented thinking (EOT). Research has yielded considerable evidence that the TAS-20 is a reliable and valid measure of alexithymia in normal and clinical adult samples. To date, no psychometric data concerning the use of the TAS-20 with adolescent samples are available. OBJECTIVES: The aim of the study is to provide psychometric data concerning the TAS-20 when administered to healthy adolescents. Furthermore, in a developmental perspective, this study explores the evolution of alexithymia across age groups in adolescence. METHOD: The TAS-20 was administered to a sample of 264 adolescents aged from 14 to 19 years. In order to compare alexithymia across age groups, the sample was divided into three groups: group 1 (<16 years old), group 2 (16-17 years old) and group 3 (>17 years old). RESULTS: Results of a confirmatory factor analysis (CFA) confirmed that the data fitted well to the three-factor model of the TAS-20 (chi(2)/df=2.22, GFI=0.88, AGFI=0.84 and RMSEA=0.068). The internal reliability coefficients and mean interitem correlations are acceptable for DIF (alpha>0.60; mean interitem correlation=0.22) and good for DDF (alpha>0.70, mean interitem correlation=0.33). As often reported in most translations of the TAS-20, the internal reliability of EOT is poor. Results of a one-way Anova showed a significant linear trend indicating that, with age, the level of alexithymia (TAS-20 total score), the difficulty in identifying feelings and the externally oriented thinking decreased. DISCUSSION: This study demonstrated that the TAS-20 has sufficient construct validity in a non-clinical sample of adolescents. Our results support the idea that adolescence period is associated with the development of the ability to regulate emotions.