Background: Comorbidity in bipolar disorder (BP) is common, of which anxiety disorder (AD) comorbidity has received recent attention. The aim of the present study was to find the prevalence of (current and lifetime) ADs in BP I with recent episode mania, its effect on illness severity and its treatment implications. This is unlike the convention of associating “anxiety” with depression. Here, the hierarchical diagnostic criterion of the DSM IV-TR was suspended for heuristic purpose. Materials and Methods: Consecutively admitted 102 consenting in-patients of bipolar mania were evaluated on Young Mania Rating Scale, Brief Psychiatric Rating Scale, and Hamilton Rating Scale for Anxiety, at baseline and after 45 days. When the patient became cooperative, Schedule for Affective Disorders and Schizophrenia - the lifetime version interview AD section, was conducted. Protocol for management of current acute state was kept flexible and naturalistic. All treatment details, historical bipolar illness and socio-demographic variables were collected from case record file and unstructured interview with patient and caregiver. Results: High prevalence of lifetime (70.2 percent) and moderate levels of current (29.6 percent) comorbid ADs were found. Comorbid lifetime AD was associated with more severe BP course (more past depressive episodes (P<0.001), less inter-episode recovery (P<0.01), and poorer response to acute phase treatment). Comorbid AD group needed more number of mood stabilizers for acute management (P<0.05). Conclusion: Findings illustrate the importance of this comorbidity having implications for psychiatric diagnostic systems.