Bipolar disorder (BD) is one of the most difficult to diagnose among all psychiatric disorders. BD is often misdiagnosed as recurrent depressive disorder, schizophrenia, anxiety or personality disorders. In 40% of patients BD is not detected at the first examination and in 2/3 of cases the proper diagnosis is made after about 10 years. The consequence of this condition is inadequate treatment leading to the worsening of the course of BD or increased risk of substance misuse and suicidal behavior. Those data reveal that the better detection of bipolar spectrum is strongly needed. It may be achieved by the application of the Mood Disorder Questionnaire (MDQ) in clinical practice. MDQ is a self rating questionnaire created by Hirschfeld et al. for screening of bipolar spectrum. According to previous data the usefulness of MDQ in populations of psychiatric patients (especially those with affective disorders) is unquestionable high. The significant limitation of MDQ is a relatively low sensitivity for BD type II. That's why the concomitant use of MDQ (as an excellent tool for detection of BD type I) and the other instrument characterized by the higher sensitivity for hypomania and BD type II (e.g. The Hypomania Symptom Checklist by Angst et al.) seems to be the best and recommended solution. This article describes the properties and structure of MDQ. The capabilities, advantages and limitations of MDQ were also presented. The authors discussed the results of validation studies of different language versions of MDQ and Summarized - DEP-BI and TRES-DEP - Polish studies using MDQ.