Inclusion Criteria:

   1. Outpatients between 3.0 and 12.11 years of age inclusive

   2. Males and females who are physically healthy

   3. diagnosis of autism based Diagnostic and Statistical Manual (DSM-IV-TR) criteria, the
   Autism Diagnostic Interview-Revised, and expert clinical evaluation

   4. Clinical Global Impression Severity rating of 4

   5. Care provider who can reliably bring subject to clinic visits, can provide trustworthy
   ratings, and interacts with subject on a regular basis

   6. Ability of subject to swallow the compound

   7. Stable concomitant medications for at least 2 weeks

   8. No planned changes in psychosocial interventions during the open-label N-Acetyl
   Cysteine trial

Exclusion Criteria:

   1. DSM-IV-TR diagnosis of schizophrenia, schizoaffective disorder, or psychotic disorder
   not otherwise specified

   2. Prior adequate trial of N-Acetyl Cysteine

   3. Active medical problems: unstable seizures, significant physical illness (e.g.,
   serious liver or renal pathology)

   4. Pregnancy or sexually active females

   5. Subjects taking antioxidant agents and glutathione prodrugs will be excluded from the
   study except if they have been off these compounds for at least 4 weeks