Previous work has demonstrated that patients with borderline personality disorder (BPD) show some similarities to patients with major depression, especially regarding their sleep profile. This study aimed at investigating such a hypothesis in an Egyptian sample, considering the possible influence of cultural differences. All night polysomnographic assessments were made for 20 ICD-10 diagnosed borderline patients (without co-morbid depression; mean age 27 yrs), in addition to 20 patients with major depression (mean age 27.8 yrs) and 20 healthy controls. The two patient groups differed significantly from controls in their sleep profile, especially regarding sleep continuity measures, decreased slow wave sleep (SWS) and REM sleep abnormalities. High similarity was found in EEG sleep profile of the two patient groups, though the changes were more robust in patients with depression. The small number of subjects precluded finer analyses of sleep microstructure by depressive symptoms. The great similarity in EEG sleep profile between BPD patients and patients with major depression suggests a common biological origin for both conditions, with the difference being 'quantitative' rather than 'qualitative'.