This randomized, double-blinded, placebo-controlled study will investigate the safety, tolerability, and pharmacokinetics of multiple doses of RO5545965 administered orally to psychiatrically stable patients with schizophrenia receiving risperidone.

Inclusion Criteria:

• Males or females aged >/= 18 years and </= 60 years
• Clinically stable, mild or moderate schizophrenia
• On stable antipsychotic treatment for the last 6 months
• Generally healthy in the investigator's opinion, based on assessment of medical history, physical examination, vital signs, electrocardiogram (ECG), and the results of the hematology, clinical chemistry, urinalysis, serology, and other laboratory tests
• Willingness to be hospitalized for approximately 3 weeks
• BMI > 18.5 kg/m2 and < 38 kg/m2
• Use of highly effective contraception as defined by the study protocol. Men must also not donate sperm until at least 30 days after the last dose, and women cannot be pregnant or breastfeeding

Exclusion Criteria:

• Treatment with antiparkinson medication including anticholinergic drugs
• Treatment with depot antipsychotic medication within the last three months prior to screening
• Participation in a clinical trial with an investigational drug or device < 3 months prior to screening
• Smokes more than 20 cigarettes per day
• Current drug abuse (excluding nicotine) or drug abuse within 3 months prior to the screening visit
• Any donation of blood or significant blood loss within three months prior to first administration of the study drug
• Use of prohibited medications (including vitamins or herbal remedies) taken within 14 days or within 5 times the elimination half-life of the medication (whichever is longer) before the first study drug administration