A Study Comparing AIN457 to Placebo in Subjects With a Diagnosis of Moderate to Severe Stable Plaque Psoriasis

Inclusion Criteria: * Males or females, aged 18-69 at time of consent. * Post menopausal or surgically sterile female patients are allowed. Male patients must be willing to use contraception method at least for 3 months following the completion of the study. Women of child-bearing potential will not be allowed to participate. * Diagnosis of plaque psoriasis for at least 6 months prior to screening. The patients must meet both of the following criterion: 1. Coverage of the body surface area (BSA) of 10% or more with plaques 2. A score of 3 or more on the IGA scale * Stable plaque psoriasis at screening and randomization. * PASI score of 12 or greater at randomization. * Able to communicate well with the investigator, and to understand and comply with the requirements of the study. Understand and sign the written informed consent. * Patients must have normal laboratory values for screening laboratory test results of hematological (hemoglobin, WBCs, neutrophils, platelets) and renal (serum creatinine) assessments. For the transaminases, aspartate aminotransferase and alanine aminotransferase, levels 1.5 times the upper limit of normal will be accepted. For the additional hepatic laboratory results (alkaline phosphatase, gamma-glutamyltransferase, bilirubin), patients must have non-clinically significant values. Exclusion Criteria: * Currently have any of the nonplaque forms of psoriasis: erythrodermic, guttate, or pustular. * Currently have drug-induced psoriasis (new onset or exacerbation of psoriasis from beta blockers, calcium channel blockers, or lithium). * Men who are planning to initiate a pregnancy while enrolled in the study or for 3 months following completion of the study. * Women of child-bearing potential are not allowed in the study. * Used any investigational drug within the previous 4 weeks. * Recent previous treatment with anti-TNF-α therapy (or other biological therapy), immunosuppressive agents such as cyclosporine, mycophenolate, pimecrolimus, or tacrolimus. The following washout period will be required for such patients to be eligible to participate in the trial. 1. 2 months washout prior to screening for etanercept, adalimumab, or infliximab. 2. 1 month washout prior to screening for cyclosporine, mycophenolate, tacrolimus, and any systemic immunosuppressants including, but not limited to, methotrexate, azathioprine, 6-thioguanine, mercaptopurine, and hydroxyurea Other protocol-defined inclusion/exclusion criteria may apply