The Meta-cognitions Questionnaire 30 (MCQ-30; Wells & Cartwright-Hatton, 2004) has been used to assess individual differences in metacognitive beliefs considered to be central in the metacognitive theory of generalized anxiety disorder (Wells, 2005). In the present study, the psychometric properties, reliability, and validity of a Spanish adaptation of the MCQ-30 were tested in a broad sample of participants (N = 768) of Spanish nationality aged 16–81 years (31.1% males, 68.9% females). Confirmatory factor analysis showed the expected five-factor structure, which was found to be invariant across gender. Internal consistency and test-retest reliability of the subscales were adequate, and the expected relationships to theoretically related variables such as pathological worry, meta-worry, thought suppression and trait anxiety were obtained. Convergent validity with other measures of beliefs about worry was also found. Taken together, these findings suggest that the Spanish version of the MCQ-30 is a valid instrument for evaluating metacognitive beliefs in the Spanish-speaking population.