The Major Depression Inventory (MDI) is a brief questionnaire to assess the presence of a depressive disorder. We prepared an Arabic version of the MDI and tested its reliability and concurrent and discriminant validity as a diagnostic tool of major depressive disorder. A group of 50 Egyptian outpatients with major depressive disorder (assessed clinically and with the Structured Clinical Interview for DSM-IV-TR Axis I Disorders) were compared with 50 healthy controls using the MDI-A, Beck Depression Inventory (BDI) and Spielberger State-Trait Anxiety Inventory (STAI). Cronbach α was 0.91 and intraclass correlation coefficient was 0.98 (95% CI: 0.97-0.99). Scores on the MDI-A strongly correlated with BDI scores (r = 0.81) but insignificantly correlated with STAI scores. Using the MDI scoring algorithm, the sensitivity was 88.4% and specificity 78.9%. We conclude that the MDI-A has an excellent reliability and an acceptable concurrent and discriminant validity.