Autism and other early onset developmental disorders (such as ADHD) (now often grouped together as ESSENCE for Early Symptomatic Syndromes Eliciting Neurodevelopmental Clinical Examinations) are considered to be much more common in boys than in girls. However, it has recently become apparent that many girls are missed or misdiagnosed (often as depression, anxiety, eating disorders or personality disorders) in early childhood and that the 'correct' diagnosis is not made until adolescence or adulthood, while an increasing number of boys are diagnosed as early as pre-school age. This means that girls do not have access to appropriate help and understanding, with a high risk of psychiatric morbidity and social maladjustment from adolescence onwards. In this unique project, clinical picture and brain function will be examined in detail in young girls and boys and adult women and men with autism and other ESSENCE problems. The aim is to find early symptoms and biological markers of autism and other ESSENCE so that girls can also receive correct early diagnosis and treatment/support interventions from pre-school age onwards. The very latest technology in clinical child and adolescent psychiatry, psychometrics, brain imaging and neurophysiology will be used. The children/adults with autism and other ESSENCE included in the project come from the Gillberg Center's world-unique population-based cohorts of individuals with childhood neuropsychiatric disabilities.