This volume is the research component and contains three papers. The first paper is a review of the literature from 1980 to the present day, which has examined intellectual, behavioural and psychological characteristics in participants with Sotos syndrome. The second paper is an empirical study which examines the behavioural phenotype of participants with Sotos syndrome in comparison to 3 other genetic syndromes using standardised, well validated questionnaires. The third paper summarises these in language accessible to the general public.