In light of the rapidly growing awareness of the link between nutrition and child and adolescent mental disorders, several recent therapeutic and preventive interventions have focused on specific supplements (e.g. vitamins and long-chain omega-3 polyunsaturated fatty acids) and diets with regard to mental health. First, associations of specific somatic disorders (including obesity, underweight, bowel problems, eczema etcetera) and child and adolescent onset psychiatric disorders (autism spectrum disorder,attention deficit hyperactivity disorder) will be presented to pave the way for the further lectures on the role of nutrition and psychiatric symptoms. Subsequently, the focus will be on specific supplements: Summarizing results from observational and randomized controlled studies an overview is provided about the physiology of n-3 LC-PUFA, the potential mechanisms which may link the n-3 LC-PUFA status with mental disorders, and the current evidence of the effects of supplementation on the symptomatology of mental disorders. With regard to vitamin D, an overview of existing evidence for deficiencies in relation to child and adolescent onset mental disorders, therapeutic effects of supplementation and potential detrimental effects of overdosing will be given. Elimination diets and their proposed mechanisms will be discussed in the light of mental health in children and adolescents: What foods are usually excluded? What are the long term effects? Finally, an overview will be provided about the gut-microbiota-brain axis and its impact on mental health in children and adolescents with attention deficit hyperactivity disorder.