Asperger's is defined in section 299.80 of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) as:

1. Qualitative impairment in social interaction, as manifested by at least two of the following:
   • Marked impairments in the use of multiple nonverbal behaviors such as eye-to-eye gaze, facial expression, body posture, and gestures to regulate social interaction
   • Failure to develop peer relationships appropriate to developmental level
   • A lack of spontaneous seeking to share enjoyment, interest or achievements with other people (e.g., by a lack of showing, bringing, or pointing out objects of interest to other people)
   • A lack of social or emotional reciprocity
2. Restricted repetitive and stereotyped patterns of behavior, interests and activities, as manifested by at least one of the following:
   • Encompassing preoccupation with one or more stereotyped and restricted patterns of interest that is abnormal either in intensity or focus
   • Apparently inflexible adherence to specific, nonfunctional routines or rituals
   • Stereotyped and repetitive motor mannerisms (e.g., hand or finger flapping or twisting, or complex whole-body movements)
   • Persistent preoccupation with parts of objects.
3. The disturbance causes clinically significant impairments in social, occupational, or other important areas of functioning.
4. There is no clinically significant general delay in language (e.g., single words used by age two years, communicative phrases used by age three years)
5. There is no clinically significant delay in cognitive development or in the development of age-appropriate self-help skills or adaptive behavior (other than in social interaction) and curiosity about the environment in childhood
6. Criteria are not met for another specific Pervasive Developmental Disorder or Schizophrenia.

Please read the DSM cautionary statement.

The Diagnostic and Statistical Manual's diagnostic criteria have been roundly criticized for being vague and subjective: what one psychologist calls a "significant impairment" another psychologist may call insignificant.