Fidgeting may be a motor sign reflecting self-regulation processes in patients with social anxiety disorder (SAD) and depressive patients. Since SAD co-occurs with comorbid depression, the question arises whether fidgeting is a disorder-unspecific phenomenon or a specific and therefore diagnostically relevant sign of depression. 33 SAD patients with (n = 12) and without (n = 21) depression from the Social Phobia Psychotherapy Research Network project were compared regarding their nonverbal behavior. Four video sequences of a psychotherapy session with each patient were analyzed using a standardized system for the analysis of nonverbal behavior by two independent, certified, blind raters. SAD patients with comorbid depression exhibited significantly more (number/minute) irregular movements, but fewer (number/minute) repetitive movements than SAD patients without depression. Irregular movements, which reflect less structured motor behavior, are associated with comorbid depression in SAD. In contrast, in SAD without depression, more structured repetitive movements were prominent. Thus, irregular movements represent a diagnostically relevant behavior for comorbid depression among SAD patients.