Paliperidone is an extended-release tablet. Paliperidone is an active metabolite of risperidone, not approved for the treatment of schizophrenia in Japan. This is a multicenter, open-label, parallel-group, fixed dose study to evaluate the safety, effectiveness, and plasma concentration of paliperidone taken once daily in patients with schizophrenia. The patients will receive a fixed dose of paliperidone (3, 9, and 15 mg) for 6 weeks and its effectiveness and safety will be observed for an additional 2 weeks.. Efficacy will be measured by determining changes throughout the study in the Positive and Negative Syndrome Scale (PANSS) score, a scale for the measurement of symptoms of schizophrenia, and the Clinical Global Impression (CGI) score. In addition, the study also assesses the relationship between dose/plasma drug concentration and dopamine D2 receptor occupancy in patients who consent to receive positron emission tomography (PET). Safety evaluations (symptoms, physical exams, electrocardiograms, laboratory tests, Drug-Induced Extrapyramidal Symptoms Scale [DIESS] results, and adverse event monitoring) will be conducted throughout the study. The study hypothesis is that paliperidone will be effective in the treatment of schizophrenia, and that it will be well-tolerated. The patients will receive either 3, 9, or 15 mg of paliperidone, taken once daily by mouth for 6 weeks.