Objective: Previous studies have focused on the relationship between childhood separation anxiety disorder (SAD) and adult panic disorder (PD)-agoraphobia. It is not clear enough whether SAD, which continues into adulthood, is associated with PD with and without comorbid agoraphobia in adult patients. Our primary hypothesis was that PD patients with comorbid agoraphobia had a higher rate of SAD that continues into adulthood than those without agoraphobia. We also hypothesized that adulthood SAD symptoms were more likely to be associated with PD-agoraphobia than PD without agoraphobia.Method: 151 patients who were diagnosed with PD with (n = 106), and without comorbid agoraphobia (n = 45) were compared using Panic and Agoraphobia Scale, Structured Clinical Interview for Separation Anxiety Symptoms, Separation Anxiety Symptom Inventory, Adult Separation Anxiety Questionnaire, and State-Trait Anxiety Inventory. We performed Student's t-test, Pearson correlation test, and multiple linear regression analysis in this study.Results: PD patients with comorbid agoraphobia were more likely to have SAD both in childhood and adulthood (p = .028), than those without agoraphobia. There were mild to moderate significant correlations between PD severity and state anxiety (p = .002), trait anxiety (p = .006), and SAD in childhood (p = .049), and in adulthood (p = .001). SAD in adulthood (β = 0.278, Exp(B) = 0.136, p = .003), and state anxiety (β = 0.236, Exp(B) = 0.164, p = .012) significantly predicted the severity of PD in patients with comorbid agoraphobia.Conclusion: SAD that continues in adulthood may be related to the severity of PD in patients with agoraphobia. Our findings might provide some evidence of the role of SAD in adulthood in patients with adult-onset PD-agoraphobia.