Trait mindfulness has received considerable attention in recent years because several studies indicate that the training in mindfulness reduces the symptoms of several psychological problems such as depression. Recently, the training in mindfulness has been extended to samples of adolescents. Therefore, the measurement of trait mindfulness in adolescents has become relevant. In this study the psychometric properties of the Mindful Attention Awareness Scale-Adolescents (MAAS-A) are evaluated in Spanish adolescents. For this purpose, 1215 adolescents (597 girls and 618 boys) aged between 14 and 18 years old participated in this study. The adolescents completed the MAAS-A and measures of depression, antisocial behavior, anger, drug abuse and lack of self-control. The results confirm the one-factor structure of the MAAS-A. The trait of mindfulness is negatively correlated with symptoms of depression, antisocial behavior, anger, drug abuse and lack of self-control. Furthermore, the adolescents who display severe depressed mood score significantly lower on mindfulness than the adolescents without symptoms or with mild and moderate depressive mood.