Assess GSK Biologicals' MMR Vaccine (Priorix) When Given to Healthy Children at the Age of 12 to 18 Months in Singapore.

Inclusion Criteria: * A male or female infant between 12 and 18 months of age at the time of the vaccination * Written informed consent obtained from the parents or guardians of the subject. * Free of obvious health problems as established by medical history and clinical examination before entering into the study. Exclusion Criteria: * Use of any investigational or non-registered drug or vaccine other than the study vaccine(s) during the study period or within 30 days preceding the dose of study vaccine * Previous vaccination against mumps and/or rubella * History of, or intercurrent, measles, mumps, and/or rubella disease * Known exposure to measles, mumps or rubella within 30 days prior to the start of the study * Any confirmed or suspected immunosuppressive or immunodeficient condition, including human immunodeficiency virus (HIV) infection.