• Clinical Global Impressions [ Time Frame: Weekly ] [ Designated as safety issue: No ]
• Aberant Behavior Checklist [ Time Frame: Weekly ] [ Designated as safety issue: No ]
• Treatment Emergent Symptoms Scale [ Time Frame: Weekly ] [ Designated as safety issue: Yes ]
• Olanzapine Untoward Effects Checklist [ Time Frame: Weekly ] [ Designated as safety issue: Yes ]
• Abnormal Involuntary Movement Scale [ Time Frame: Weekly ] [ Designated as safety issue: Yes ]
• Neurological Rating Scale [ Time Frame: Weekly ] [ Designated as safety issue: Yes ]

This is a 12-week study which investigates the use of olanzapine to decrease disruptive behaviors sometimes associated with Autism in children, aged 3 to 12 years old. The first six weeks of the study are double-blind and placebo controlled, meaning that patients receive either placebo or olanzapine, and that neither the researchers nor the patients know whether or not they are receiving placebo or olanzapine. In the second six weeks all of the patients receive olanzapine. The purpose in using placebo is that it is otherwise impossible to know how effective the drug is or whether or not the drug causes side effects. Patients treated with placebo can have improvement and can have side effects. In the study patients receive a psychiatric evaluation, physical examination, laboratory tests, and study medication (olanzapine or placebo), free of charge.

• Drug: olanzapine (Zyprexa)
• Drug: Placebo

• Experimental: Treatment with olanzapine
• Placebo Comparator: Matching placebo treatment

Inclusion Criteria:

1. Males and females, Aged between 3 and 12 years.
2. Autistic disorder - DSM-IV criteria.
3. A score of at least moderately impaired on the CGI-Severity item.
4. Clinical judgment that medication treatment for autism is indicated.

Exclusion Criteria:

1. Rett's disorder, childhood disintegrative disorder, Asperger's disorder, and PDD, NOS.
2. Psychotic disorder (DSM-IV) (including schizophreniform disorder and schizophrenia).
3. Major depressive disorder (DSM-IV).
4. Bipolar disorder (DSM-IV).
5. History of psychoactive drug in the previous 2 weeks prior to phase 1.
6. A history of treatment with olanzapine for a cumulative period of greater than 2 weeks prior to entering phase 1.
7. Systemic diseases such as cardiac, renal, thyroid diseases, uncontrolled seizure disorder (seizure disorder that is not controlled by anti-epileptic medication - a child who is seizure free for a period of 6 months on a stable dose of antiepileptic drug would be considered controlled), or diabetes mellitus.
8. Children with a known medical cause for autistic disorder.
9. Abnormal fasting blood glucose or history of diabetes.
10. Baseline body mass index (BMI) greater than the 90th percentile for age and gender (CDC growth charts, Kuczmarski et al, 2000) (because of risk of weight gain).
11. Baseline QTc >450 msec. Note: Historically, patients we evaluate do not have QTc values >450.
12. Dyskinesias at baseline (per the criteria of Schooler and Kane, 1982).