Objective: In the present study, we compared social anxiety disorder (SAD) patients with (n = 31) and without childhood and adulthood separation anxiety disorder (SeAD) (n = 50) with respect to suicidal behavior, avoidant personality disorder (AvPD), other anxiety disorders (ADs), and major depression as well as some sociodemographic variables. Methods: In assessment of patients, we used Structured Clinical Interview for Separation Anxiety Symptoms, childhood and adulthood Separation Anxiety Symptom Inventories, Liebowitz Social Anxiety Scale, The SCID-II Avoidant Personality Disorder Module, Beck Depression Inventory, and Beck Scale for Suicidal Ideation. Results: SAD patients with SeAD had higher comorbidity rates of AvPD, other lifetime ADs and panic disorder, and current major depression than those without SeAD. The current scores of SAD, depression, and suicide ideation and the mean number of AvPD symptoms were significantly higher in comorbid group compared to pure SAD subjects. The SAD and SeAD scores had significant associations with current depression, suicide ideations, and AvPD. The mean number of AvPD criteria and the current severity of depression were significantly associated with the comorbidity between SAD and SeAD. Conclusion: Our findings might indicate that the comorbidity of SeAD with SAD may increase the risk of the severity of AvPD and current depression.