Autism is a developmental disorder characterized by difficulties with social interaction and communication, and by restricted and repetitive behavior.[6] Parents often notice signs during the first three years of their child's life.[1][6] These signs often develop gradually, though some children with autism experience worsening in their communication and social skills after reaching developmental milestones at a normal pace.[17]

Autism is associated with a combination of genetic and environmental factors.[7] Risk factors during pregnancy include certain infections, such as rubella, toxins including valproic acid, alcohol, cocaine, pesticides, lead, and air pollution, fetal growth restriction, and autoimmune diseases.[18][19][20] Controversies surround other proposed environmental causes; for example, the vaccine hypothesis, which has been disproven.[21][22] Autism affects information processing in the brain and how nerve cells and their synapses connect and organize; how this occurs is not well understood.[23] The Diagnostic and Statistical Manual of Mental Disorders (DSM-5), combines autism and less severe forms of the condition, including Asperger syndrome and pervasive developmental disorder not otherwise specified (PDD-NOS) into the diagnosis of autism spectrum disorder (ASD).[6][24]

Early behavioral interventions or speech therapy can help children with autism gain self-care, social, and communication skills.[9][10] Although there is no known cure,[9] there have been cases of children who recovered.[25] Some autistic adults are unable to live independently.[15] An autistic culture has developed, with some individuals seeking a cure and others believing autism should be accepted as a difference to be accommodated instead of cured.[26][27]

Globally, autism is estimated to affect 24.8 million people as of 2015.[16] In the 2000s, the number of people affected was estimated at 1–2 per 1,000 people worldwide.[28] In the developed countries, about 1.5% of children are diagnosed with ASD as of 2017,[29] from 0.7% in 2000 in the United States.[30] It occurs four-to-five times more often in males than females.[30] The number of people diagnosed has increased dramatically since the 1960s, which may be partly due to changes in diagnostic practice.[28] The question of whether actual rates have increased is unresolved.[28]