The purpose of the study is to determine whether, in patients with moderate to severe plaque-type psoriasis, AIN457 administered subcutaneously reduces the severity of psoriasis symptoms and the extent to which the patient's body area is affected by the disease (compared to placebo).

Inclusion Criteria:

Chronic plaque-type psoriasis diagnosed for at least 6 months at time of randomization

At randomization, moderate to severe psoriasis as defined by:

• PASI score of 12 or greater and,
• IGA score of 3 or greater and,
• Body Surface Area (BSA) affected by plaque-type psoriasis of 10% or greater At screening and randomization, chronic plaque-type psoriasis considered inadequately controlled by topical treatment.

Exclusion Criteria:

• Forms of psoriasis other than chronic plaque-type
• Drug-induced psoriasis (e.g., new onset or current exacerbation from beta-blockers, calcium channel inhibitors or lithium) at randomization
• Previous exposure to AIN457
• Ongoing use of prohibited psoriasis treatments / medications and other prohibited medication at randomization. Washout periods detailed in the protocol have to be adhered to
• Known immunosuppression (e.g., AIDS) at screening and / or randomization
• History or evidence of active tuberculosis at screening
• Active systemic infections (other than common cold)
• History or symptoms of malignancy of any organ system, treated or untreated, within the past 5 years.
• Any severe, progressive or uncontrolled medical condition at randomization that in the judgment of the investigator prevents the patient from participating in the study
• Any clinically significant abnormal laboratory tests at randomization, that in the judgment of the investigator prevents the patient from participating in the study
• Inability or unwillingness to undergo repeated venipuntures
• History or evidence of drug or alcohol abuse
• Pregnant or nursing (lactating) women

Other protocol-defined inclusion/exclusion criteria may apply