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Backgound: Almost all cases of DiGeorge syndrome, velo-cardio-facial syndrome and conotruncal anomaly face syndrome result from a common deletion of chromosome 22q11.2. These syndromes are usually referred to as the 22q11 deletion syndrome (22q11DS), which has a wide phenotypic spectrum and an estimated incidence of one in 4000 births. Aims: To assess the incidence and prevalence of the 22q11 deletion syndrome in the Western Götaland Region of western Sweden Methods: Children below 16 years of age with 22q11DS in a well defined catchment area and population of the Western Götaland Region were recruited. Diagnosis of 22q11DS was confirmed using a FISH (fluorescence in situ hybridisation) test. Proven 22q11 deletion was the demonstration of one signal in 11 metaphase spreads with fair quality. Results: During the study period in the Western Götaland Region the mean annual incidence of 22q11DS was 14.1 per 100 000 live births. During the first five years the incidence was 18.1 per 100 000 live births for the whole region and 23.4 per 100 000 live births in Gothenburg, where a multidisciplinary specialist team for 22q11 DS is based. The prevalence was 13.2 per 100 000 children below 16 years of age in the whole region and 23.3 per 100 000 in Gothenburg