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The Tourette Syndrome International Database Consortium began in 1992 as a collaborative project between two centres in Canada and one in the USA, and now collects data from 65 centres in 22 countries on six continents. A recent report (Roger D Freeman and colleagues. Developmental Medicine and Child Neurology 2000;42:436–47) includes information on 3500 people with Tourette syndrome. There was a preponderance of males at all centres, the overall male:female ratio being 4.3:1. Tics began in all cases before the age of 20, in 41% before 6 years, and in 93% before 10 years. The diagnosis was made before the age of 10 in 56% and before the age of 15 in over 80%. In only 12% of cases was Tourette syndrome the only diagnosis; other diagnoses included attention deficit hyperactivity disorder (60%), obsessive compulsive disorder (27%), obsessive compulsive behaviour (32%), learning disorder (23%), and conduct disorder/oppositional defiant disorder (15%). The number of comorbid disorders (in addition to Tourette syndrome) ranged from none to six (average two) and they strongly influenced the likelihood of behavioural problems—such as, anger control problems, coprolalia, self injury, and sleep difficulties, all of which were much more likely to occur with an increasing number of comorbid diagnoses. Thus, uncontrolled anger occurred in around 5% of those with Tourette syndrome alone, about 40% of those with three additional diagnoses, and over 70% of those with six additional diagnoses. Behavioural problems in people with Tourette syndrome should lead to renewed assessment for additional psychiatric diagnoses. Treatment of these comorbid conditions may be as important as treatment of the tics (or more important). The existence of this large database should facilitate future research.