Those who stutter have a proclivity to social anxiety. Yet, to date, there is no comprehensive measure of thoughts and beliefs about stuttering that represent the cognitions associated with that anxiety.The present paper describes the development of a measure to assess unhelpful thoughts and beliefs about stuttering.The Unhelpful Thoughts and Beliefs about Stuttering (UTBAS) self-report measure contains 66 items that assess the frequency of unhelpful thoughts and beliefs. Items were constructed from a comprehensive file audit of all stuttering cases seen in a cognitive-behavior therapy based treatment programme over a ten-year period.Preliminary investigations indicate that the UTBAS has high levels of test-retest reliability (r = 0.89) and internal consistency (Chronbach's alpha = 0.98). It has good known-groups validity, being able to discriminate between stuttering and non-stuttering participants on items that contain no reference to stuttering [t(38) = 8.06, p<0.0001], with a large effect size (d = 2.3). It has good convergent validity (r = 0.53-0.72) and discriminant validity (r = 0.24-0.27). The UTBAS sensitivity to change was supported by improvements in thoughts and beliefs related to social anxiety following cognitive-behavioural treatment for anxiety in stuttering [t(25) = 10.13, p<0.0001]. The effect size was large (d = 2.5).Implications for the use of the UTBAS as an outcome measure and a clinical tool are discussed, along with the potential value of the UTBAS to explore the well-documented social anxiety experienced by those who stutter.