AbstractObjectiveThis article describes the development and psychometric evaluation of the Manic Thought Inventory (MTI), a patient‐driven self‐report inventory to assess the presence of typical (hypo)manic cognitions.MethodsThe initial item pool was generated by patients with bipolar disorder (BD) type I and assessed for suitability by five psychiatrists specialized in treating BD. Study 1 describes the item analysis and exploratory factor structure of the MTI in a sample of 251 patients with BD type I. In study 2, the factor structure was validated with confirmatory factor analysis, and convergent and divergent validity were assessed in an independent sample of 201 patients with BD type I.ResultsStudy 1 resulted in a 50‐item version of the MTI measuring one underlying factor. Study 2 confirmed the essentially unidimensional underlying construct in a 47‐item version of the MTI. Internal consistency of the 47‐item version of the MTI was excellent (α = 0.97). The MTI showed moderate to large positive correlations with other measures related to mania. It was not correlated with measures of depression.ConclusionThe MTI showed good psychometric properties and can be useful in research and clinical practice. Patients could use the MTI to select items that they recognize as being characteristic of their (hypo)manic episodes. By monitoring and challenging these items, the MTI could augment current psychological interventions for BD.