Objectives : It is reported that panic disorder is frequently comorbid with other psychiatric illnesses. The aim of this study was to investigate differences of psychiatric comorbidity according to age of onset of panic disorder. Methods : Three hundred-two patients participated in the study. All the patients were evaluated by clinical instruments for the assessment the presence of other comorbid psychiatric disorders and various clinical features; Korean version of Mini International Neuropsychiatric Interview, Self-report questionnaires(Beck Anxiety Inventory, Beck Depression Inventory, Anxiety Sensitivity Index and State-Trait Anxiety Inventory) and clinical rating scale (Hamilton Anxiety Scale, Hamilton Depression Scale and Global Assessment of Functional score). Chi-square test was used to determine the difference between early onset and late onset panic disorder. Results : Forty percent of panic patients were found to have at least one comorbid psychiatric diagnosis. There were no differences among the groups divided by number of comorbidity in sex, agoraphobia comorbidity, duration of panic disorder, except onset age of panic disorder. Early onset group had more comorbidy with social phobia, agoraphobia, PTSD. We also found that Early onset panic disorder patients were more likely to experience derealization, nausea, parethesia than late onset panic disorder patients. Conclusion : The results of our study are in keeping with previous data from other parts of the world. Our finding suggest that earier onset of panic disorder related to more psychiatric comorbidity.