Background <p>The Metacognition Questionnaire, including the version adapted to adolescents, measures non-adaptive metacognition believes. This study measured the structure of the MCQ-A factor in adolescents, and its correlation with anxiety and emotional regulation.</p> Objective <p>The aim of this study was the adaptation and validation of the Spanish version of the questionnaire on metacognitive beliefs in adolescents with a sample of schoolchildren (<i>N</i> = 1031, age = 14.91 years).</p> Methods <p>Two studies were undertaken: (1) the translation of the MCQ-A scale into Spanish, including the evaluation of internal consistency, factorial structure, and convergent validity; and (2) the confirmatory factorial analysis of the questionnaire.</p> Results <p>Five factors were obtained: (1) positive beliefs about concerns; (2) negative beliefs about lack of control and concern risk; (3) cognitive confidence; (4) the need to control thoughts; and (5) cognitive self-awareness. The exploratory factorial analysis clearly showed that the MCQ-A scale factors present an aggregate variance of 53.42%, which explains the unique variation of metacognitive beliefs. For its part, confirmatory factorial analysis endorsed the suitability of the model, with a sustainable structure that comprise the five factors identified and 30 items. In addition, network analysis revealed that metacognitive beliefs and feature-anxiety are related.</p> Conclusion <p>The MCQ-A is easy to understand and fast to complete, so it is regarded as useful for the assessment of non-adaptive metacognitive beliefs in adolescents.</p>