This review on autism spectrum disorder (ASD) focusses on recent insights in the clinical picture, such as continuity of the phenotype and the concept of broader phenotype, on epidemiology and on clinical issues relevant to physicians, including new methods for early screening and diagnosis, psychiatric and somatic co-morbidity, and the expansion of so-called complementary and alternative treatments. ASD is a disorder with mainly genetic causes and recent insights show that a variety of genetic mechanisms may be involved, i.e. single gene disorders, copy number variations and polygenic mechanisms. Technological advances in genetics have lead to a number of promising findings, which, together with other lines of fundamental research, suggest that ASD may be a disorder of connectivity in the brain, at least in a subgroup of patients. It is possible that part of the genetic load in autism actually reflects gene-environment interaction, but there is no evidence for purely environmental causes in a substantial number of cases. Clinical research suggests that ASD may be a multi-system disorder in at least a subgroup of subjects, affecting the gastro-intestinal (GI) tract, the immune system and perhaps other systems. Behavioural treatments remain the cornerstone of management, and are mainly aimed at stimulation of the domains of impaired development and reducing secondary behaviours. These treatments are constantly being refined, but the main progress in this area may be the increase of research on effectiveness.