Background: In an initial validation study, the Unhelpful Thoughts and Beliefs About Stuttering (UTBAS I) scale, demonstrated excellent psychometric properties as a self-report measure of the frequency of unhelpful cognitions associated with social anxiety for adults who stutter. Aims: The aim was to further validate the original UTBAS I scale, and to develop two additional scales to assess beliefs (UTBAS II) and anxiety (UTBAS III) associated with negative thoughts. Methods & Procedures: A total of 140 adults seeking speech-restructuring treatment for stuttering completed the original UTBAS I scale, the newly developed UTBAS II and III scales, and self-report measures of psychological functioning. Participants also completed a first-stage screener for the presence of anxious personality disorder, and a diagnostic assessment to evaluate the presence of social phobia, according to criteria of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) and the International Classification of Diseases (ICD-10). Outcomes & Results: The mean UTBAS I score for the present sample did not differ significantly from the mean score reported in the original UTBAS I validation study. Convergent validity was confirmed by significant correlations between the UTBAS Total score and all anxiety-related measures. Discriminant validity was established by the absence of strong correlations between the UTBAS Total score and some of the self-report measures of unrelated constructs, although it was found to tap into the negative cognitions associated with depression and life problems. Approximately one-quarter of participants met criteria for a diagnosis of DSM-IV or ICD-10 social phobia (23.5% and 27.2% respectively), and nearly one-third met first-stage screening criteria for anxious personality disorder (30%). The mean UTBAS scores for participants who met criteria for these disorders were significantly higher than scores for participants who did not, confirming known-groups validity. Conclusions & Implications: The present study demonstrates the validity and utility of the UTBAS scales in assessing negative cognitions associated with speech-related anxiety among adults who stutter. Results also confirm previous evidence of a high rate of social phobia among adults who stutter, and reveal that the UTBAS discriminates between adults with and without social phobia. In terms of clinical applications, the UTBAS scales could be used to screen for indicators of social phobia among adults who stutter, and may prove useful in identifying negative cognitions which have the potential to impact treatment outcomes.