The purpose of this study is to explore the efficacy of paliperidone palmitate administered as a once monthly injection in patients with an acute exacerbation of schizophrenia.

This is an open-label (patients and study staff will know the identity of treatments assigned) study of paliperidone palmitate in patients with acute an exacerbation of schizophrenia. The total duration of the study will be approximately 4 months. Eligible patients without a documented history of exposure to oral risperidone or paliperidone extended-release (ER), or intramuscular (IM) RISPERDAL CONSTA or paliperidone palmitate will receive oral risperidone 1 mg/day or extended release (ER) OROS paliperidone 3 mg/day for at least 3 days before the first injection of the study drug (paliperidone palmitate) for tolerability testing. Paliperidone palmitate will be administered to patients as an intramuscular (IM) injection in the deltoid (upper arm) or gluteal (buttocks) muscle.

Inclusion Criteria:

• Be otherwise healthy on the basis of physical examination and vital signs at Screening (Baseline) and have a current diagnosis of schizophrenia according to Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) for at least 1 year before screening and no longer than 5 years (early diagnosed patients)
• Have acute exacerbation of psychosis defined as: less than 4 weeks but more than 4 days, PANSS total score of 70 to 120 (inclusive) at screening (moderate symptomatology), a score of 4 or more (at least moderately ill) at screening on the severity scale of the CGI-S
• If a woman, before entry she must be postmenopausal for at least 1 year, surgically sterile or abstinent. If sexually active, agree to practice an effective method of birth control before entry and throughout the study as specified in the protocol; If a man is heterosexually active with a woman of childbearing potential, he must agree to use a double-barrier method of birth control and to not donate sperm during the study and for 50 days after receiving the last dose of the study drug

Exclusion Criteria:

• Has evidence of clinically significant cardiovascular, renal, hepatic, gastrointestinal, neurological, endocrine, metabolic or pulmonary disease in the past 6 months (as determined by medical history, clinical laboratory or electrocardiogram [ECG] results, or physical examination) that would increase the risk associated with taking study medication or would confound the interpretation of the study
• The psychiatric diagnosis is due to direct pharmacological effects of a substance (eg, a drug of abuse or medication) or a general medical condition (eg, clinically notable hypothyroidism, delirium)
• Meets the DSM-IV definition of substance dependence (except for nicotine and caffeine) within 6 months prior to entry
• Has history or current symptoms of tardive dyskinesia (involuntary repetitive body movements)
• Has history of neuroleptic malignant syndrome