This study will assess the efficacy, safety and tolerability of AFQ056 when added to optimize standard therapy in patients that have Huntington's disease in reducing chorea.

Inclusion Criteria:

• Huntington's disease (based on DNA testing polyQ >36) with a UHDRS maximal chorea score of >10
• patient with concomitant Huntington's medication (anti-depressants, neuroleptics, benzodiazepines) are allowed but the total daily dose and dosing regimen has to be stable for at least one months prior to randomization
• female patients without childbearing potential (post-menopausal or surgically sterilized), all patients must using a double-barrier local contraception

Exclusion Criteria:

• patients with marked cognitive impairment (MMSE less than 18), with presence of psychosis and/or confusional states
• patients with a history or presence of renal impairment and/or liver disease Other protocol-defined inclusion/exclusion criteria may apply