Theory of mind (ToM) is a complex cognitive mechanism which refers to our ability to understand that other people have beliefs, plans, desires, hopes, intentions, and knowledge that may differ from our own mental and emotional states. Theory of mind is critical for social and interpersonal functioning and allows people to make sense of other’s behavior. Theinitial aim of theory of mind research was to record normative development in preschool age children. Almost 30 years ago, when researchers discovered that theory of mind is altered in individuals with autism spectrum disorder, they also explored impairments in ToM in different clinical disorders. Research results indicate the presence of ToM deficits in childhood mental and neurodevelopmental disorders, such as: autism spectrum disorders, attention deficit hyperactivity disorder, oppositional defiant disorder, Gilles de la Tourette Syndrome, fetus alcohol syndrome, mood disorders, eating disorders, or obsessive-compulsive disorder. This article reviews significant studies of theory of mind impairments in individual childhood disorders and selected mental disorders.