The Metacognition, Affective, Cognitive Experience (MACE) questionnaire was designed to assess metacognition across sleep and waking (Kahan & LaBerge, 1996). The present research evaluates the psychometric properties of the MACE. Data from two recent studies (N = 185) were used to assess the inter-item consistency, test-retest reliability, and factorial, convergent, and discriminant validity of the MACE. Results show that the MACE is a reliable measure with good construct validity. Exploratory factor analyses revealed one self-regulation and two monitoring factors. One monitoring factor emphasized monitoring internal conditions; the other emphasized monitoring external conditions. This factor structure is consistent with the Metacognitive Model (Nelson & Narens, 1990). Tests of convergent and discriminant validity suggest that the MACE is assessing metacognition and is appropriately related to similar constructs such as mindfulness and self-consciousness. The implication of these findings as well as suggestions for research and clinical applications of the MACE are discussed.