Inclusion Criteria:

Subjects will be eligible for this study if they participated in the Double-blind,
randomized, placebo controlled study of N-Acetyl Cysteine in Autism study at Stanford
University and meet all of the following 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 on 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. Diagnostic and Statistical Manual (DSM-IV-TR) diagnosis of schizophrenia,
   schizoaffective disorder, or psychotic disorder, not otherwise specified

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

   3. Pregnancy or sexually active females

   4. 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