Individuals with Autistic Disorder have restricted, repetitive, and stereotyped patterns of behavior, interests, and activities.   There may be an encompassing preoccupation with one or more stereotyped and restricted patterns of interest that is abnormal either in intensity or focus (Criterion A3a); an apparently inflexible adherence to specific, nonfunctional routines or rituals (Criterion A3b); stereotyped and repetitive motor mannerisms (Criterion A3c); or a persistent preoccupation iwth parts of objects (Criterion A3d).   Individuals iwth Autistic Disorder display a markedly restricted range of interests and are often preoccupied with one narrow interest (e.g.,dates, phone numbers, radio station call letters).   They may line up an exact number of play things in the same manner over and over again or repetitively mimic the actions of a television actor.   They may insist on sameness and show resistance to or distress over trivial changes (e.g.,a younger child may have a catastrophic reaction to a minor change in the environment such as rearrangement of the furniture or use of a new set of utensils at the dinner table).   There is often an interest in nonfunctional routines or rituals or an unreasonable insistence on following routines (e.g.,taking exactly the same route to school every day).   Stereotyped body movements include the hands (clapping,finger flicking) or whole body (rocking, dipping, and swaying).   Abnormalities of posture (e.g.,walking on tiptoe, odd hand movements and body postures) may be present.   These individuals show an persistent preoccupation with parts of objects (buttons,parts of the body).   There may also be a fascination with movement (e.g.,the spinning wheels of toys, the opening and closing of doors, an electric fan or other rapidly revolving object).   The person may be highly attached to some inanimate object (e.g.,a piece of string or a rubber band).

     The disturbance must be manifest by delays or abnormal functioning in at least one (and often several) of the following areas prior to age 3 years: social interaction, language as used in social communication, or symbolic or imaginative play (Criterion B).   In most cases, there is no period of unequivocally normal development, although in perhaps 20% of cases parents report relatively normal development for 1 or 2 years.   In such cases, parents may report that the child acquired a few words and lost these or seemed to stagnate developmentally.

     By definition, if there is a period of normal development, it cannot extend past age 3 years.   The disturbance must not be better accounted for by Rett's Disorder or Childhood Disintegrative Disorder (Criterion C).

     Associated descriptive features and mental disorders.   In most cases, there is an associated diagnosis of Mental Retardation, which can range from mild to profound.  There may be abnormalities in the development of cognitive skills.   The profile of cognitive skills is usually uneven, regardless of the general level of intelligence, with verbal skills typically weaker than nonverbal skills.   Sometimes special skills are present (e.g.,a 41/2 year old girl with Autistic Disorder may be able to "decode" written materials with minimal understanding of the meaning of what is read [hyperlexia] or a 10 year old boy may have prodigious abilities to calculate dates [calendar calculation]).   Estimates of single-word (receptive or expressive) vocabulary are not always good estimates of language level (i.e.,actual language skills may be a much lower levels).