What are autism levels 1, 2, and 3?

The DSM-5 (the diagnostic manual) classifies autism into three support levels, based on two dimensions: social communication and restricted or repetitive behaviors.

Level 1, "Requiring support": without support in place, noticeable deficits cause real impairment. Usually fluent verbal communication, but with difficulties in social reciprocity and reading social nuance. Rigid behaviors that cause significant interference when disrupted. This used to be called Asperger syndrome, or high-functioning autism.

Level 2, "Requiring substantial support": marked deficits in verbal and nonverbal communication. Atypical or reduced response to others' attempts at social interaction. More limited social communication with greater difficulties. Repetitive behaviors that are harder to redirect.

Level 3, "Requiring very substantial support": severe deficits in verbal and nonverbal communication cause serious functional impairment. Very limited or absent verbal communication. Repetitive behaviors that markedly interfere across all areas of life.

Important: levels can shift over a lifetime (especially during burnout or after early intervention), a person can be at different levels in different domains, and the levels do not describe the person, only the amount of support they need at a given point in time.