Bipolar disorderis underdiagnosed. On average there is a delay of about 12 years between the onset of symptoms and a correct diagnosis of the disorder. This delay may lead to inadequate treatment. The Mood Disorder Questionnaire (MDQ) is a screening instrument to improve the detection ofbipolar disorder. Research has shown that the English version of this self-administered questionnaire has sufficient reliability and validity. A Dutch version of the MDQ (MDQ-NL) is now available. The MDQ-NL is not time-consuming for both patient and investigator and is well suited for screening. A positive test should be followed by assessment of the patient by a psychiatrist. Application of the MDQ-NL will lead to better recognition and treatment of bipolar disorder in the Netherlands.