Patients with anxiety disorder (AD) are more likely to be concurrently comorbid with other ADs or major depressive disorder (MDD). However, it is unknown whether such patients show more severe anxiety symptoms than patients with single AD. We compared anxiety severity among patients with single AD, multiple ADs, and multiple ADs plus MDD. Subjects were 136 consecutive outpatients with any AD who were comprehensively diagnosed. Symptom severity of panic disorder (PD), social anxiety disorder (SAD), obsessive-compulsive disorder (OCD), and generalized anxiety disorder (GAD) was measured using self-rating questionnaires, and the scores were compared among the 3 comorbidity conditions (single AD vs. multiple ADs vs. multiple ADs plus MDD). PD and SAD scores in the multiple ADs and the multiple ADs plus MDD conditions were significantly greater than the scores in the single AD condition regardless of diagnosis of PD and SAD. OCD scores did not differ among the 3 conditions while the scores in patients with OCD were significantly greater than those in patients without OCD. GAD scores in the multiple ADs plus MDD condition were significantly greater than those in the single AD and the multiple AD conditions. Moreover, in patients with MDD, the GAD scores in patients with GAD were not greater than those in patients without GAD. The results suggest that symptoms of PD, SAD, and GAD but not OCD are affected by the diagnosis of multiple ADs or comorbid MDD and that diagnosis of comorbid MDD affects GAD symptoms more strongly than diagnosis of GAD.