ABSTRACT: INTRODUCTION: A research commentary published in 2005 pointed out that the apparently low prevalence of Bipolar Disorder diagnosis as reported by epidemiological studies may be related to the under-estimate of bipolar disorder cases generally yielded by methodological instruments that are applied in such investigations. NEW DATA APPARENTLY CHALLENGE THIS NOTION: More recent publications have presented new results that apparently contradict the issues raised by the commentary, stating that the CIDI interview, which is used in the most important epidemiological studies is not only valid but highly reliable in identifying bipolar disorders. COMMENTARY: This paper analyzes the new data and concludes that they do not give a clear indication as to how reliably the CIDI can recognize undiagnosed bipolar disorder cases. Further research studies are needed on larger "negative" (to the CIDI) samples before the field will be persuaded that CIDI really does what it is supposed to do.