Autism is a developmental disorder characterized by troubles with social interaction and communication, and by restricted and repetitive behavior.[3]Parents usually notice signs in the first two or three years of their child's life.[1][3]These signs often develop gradually, though some children with autism reach their developmental milestones at a normal pace and then worsen.[9]

Autism is caused by a combination of genetic and environmental factors.[4] Risk factors include certain infections during pregnancy such as rubella as well as valproic acid, alcohol or cocaine use during pregnancy.[10] Controversies surround other proposed environmental causes, for example the vaccine hypotheses, which have been disproven.[11] Autism affects information processing in the brain by altering how nerve cells and their synapses connect and organize; how this occurs is not well understood.[12] In the DSM-5, autism is included within the autism spectrum (ASDs), along with Asperger syndrome, which is less severe, and pervasive developmental disorder not otherwise specified (PDD-NOS).[3][13]

Early speech or behavioral interventions can help children with autism gain self-care, social and communication skills.[6] Although there is no known cure,[6] there have been cases of children who have recovered from the condition.[14] Not many children with autism live independently after reaching adulthood, though some are successful.[7] An autistic culture has developed, with some individuals seeking a cure and others believing autism should be accepted as a difference and not treated as a disorder.[15][16]

Globally, autism is estimated to affect 24.8 million people as of 2015.[8] In the 2000s, the number of people affected was estimated at 1–2 per 1,000 people worldwide.[17] In the developed countries, about 1.5% of children are diagnosed with ASD as of 2017,[18] a more than doubling from 1 in 150 in 2000 in the United States.[19] It occurs four to five times more often in boys than girls.[19] The number of people diagnosed has increased dramatically since the 1960s, partly due to changes in diagnostic practice; the question of whether actual rates have increased is unresolved.[17]