BackgroundDepression is a prevalent psychiatric disorder that can arise at any age and is often present as a co-occurring illness in different illnesses. There is a high comorbidity rate between major depressive disorder and personality disorders (PDs). The current study aimed to investigate the significant impact of personality disorders on depression severity, functional impairment, and suicidal tendencies in individuals with depression.MethodsThe researchers conducted a cross-sectional observational study involving 120 patients, with an age range from 18 to 56 years of both genders, recruited from Okasha’s Institute of Psychiatry in Cairo, Egypt. Their major depressive disorder diagnosis was verified through the use of the Structured Clinical Interview for DSM-IV Axis I Disorders (SCID-I). Participants underwent evaluations using the SCID-II to evaluate personality disorders, the Hamilton Depression-Rating Scale (HAM-D) to assess the severity of depression, the Columbia Suicide Severity Rating Scale (C-SSRS) to investigate suicidal ideation, and the Global Assessment of Functioning Scale (GAF) to determine functional level.ResultsBorderline personality disorder and narcissistic personality disorder were the predominant personality disorders in the sample, with prevalence rates of 55.8% and 40.8%, respectively. Sixty-six percent of the participants reported experiencing suicidal thoughts at some point in their lifetime, whereas only 17.5% had actually attempted suicide. Borderline personality disorder showed a strong correlation with more severe depression (P value 0.043), a decline in functioning (P value 0.001), the existence of suicidal thoughts (P value 0.001), and a past of suicide attempts (P value 0.038).ConclusionsPersonality disorders are highly prevalent in patients with depression, borderline PD, and narcissistic PD were the most common PDs. Borderline PD showed a significant effect on depression severity. PDs, mainly borderline, avoidant, depressive, and narcissistic PDs contribute to more impairment of functioning of the MDD patients. There is a significant effect of the presence of co-morbid personality disorder on suicidal thoughts and suicidal attempts, mainly depressive and borderline PDs.