evidence: There are no specific cognitive, metabolic or neurological markers and no medical tests for ADHD. Because of uncertainty about definition, epidemiological studies produce hugely differing prevalence rates: from 0.5% to 26% of children. Despite attempts at standardising criteria, in cross-cultural studies major and significant differences between raters from different countries in the way they rate symptoms of ADHD, as well as major differences in the way children from different cultures are rated for symptoms of ADHD, are apparent. More than 30 neuroimaging studies have been published; however, researchers have yet to compare unmedicated children diagnosed with ADHD with an age-matched control group. Sample sizes in these studies have been small and have produced a variety of inconsistent results. In no study were the brains considered clinically abnormal, nor is it possible to work out whether any differences seen are caused by (rather than being the causes of) different styles of thinking, or are the result of the medication the children had taken. What we end up with is a modern version of the long-discredited ‘science’ of phrenology.