Autism spectrum disorder (ASD) is characterized by deficits in social cognition and competence, communication, highly circumscribed interests and a strong desire for routines. Besides, there are specific abnormalities in perception and language. Typical symptoms are already present in early childhood. Traditionally autism has been regarded as a severe form of neurodevelopmental disorder which goes along with overtly abnormal language, learning difficulties and low IQ in the majority of cases. However, over the last decades, it has become clear that there are also many patients with high-functioning variants of ASD. These are patients with normal language at a superficial level of description and normal and sometimes above average intelligence. In high-functioning variants of the disease, they may run unrecognized until late in adult life. High-functioning ASD is associated with a very high prevalence of comorbid classical psychiatric disorders such as depression, anxiety, ADHD, tics, psychotic symptoms or emotionally unstable syndromes. In many such cases, there is a causal relationship between ASD and the comorbid psychiatric conditions in that the specific ASD symptoms result in chronic conflicts, misunderstandings and failure in private and vocational relationships. These problems in turn often lead to depression, anxiety and sometimes psychosis-like stress reactions. In this constellation, ASD has to be regarded as a basic disorder with causal relevance for secondary psychiatric syndromes. In this paper, we summarize the classical presentation of high-functioning ASD in adult psychiatry and psychotherapy and suggest a nosological model to classify different ASD conditions instead. To conclude, we outline first treatment concepts in out- and in-patient settings.