The purpose of this study is to evaluate the effects of different atypical antipsychotics on weight changes, energy homeostasis, metabolism, energy intake as well as activity.

Patients with schizophrenia or schizoaffective disorders will be randomly assigned to be treated with ziprasidone or olanzapine for 24 weeks.

Primary outcome parameter are the weight changes after 24 weeks.

Inclusion Criteria:

• Diagnosis of schizophrenia or related disorders(DSM-IV)
• Indication for long-term treatment with antipsychotics
• BMI between 20 to 30
• Weight changes less than 3kg in the last 3 months before inclusion
• Informed consent

Exclusion Criteria:

• Psychiatric comorbidity
• Depot antipsychotic in the last 2 months
• Antipsychotics in the last 2 weeks
• Treatment with olanzapine, clozapine or ziprasidone in teh last 3 months
• Treatment with drugs, that may lead to weight changes
• Significant endocrine, neurological, cardiovascular, hepatic, renal, metabolic, or other medical diseases or any clinically relevant abnormalities in laboratory tests
• Female subjects during pregnancy and breastfeeding
• Female subjects within childbearing years who were not using adequate birth control
• Patients who are judged by the investigator to be at serious suicide risk