Introduction：A large rubella outbreak has been occurring in Tokyo, Japan since June 2012. Rubella vaccination, introduced in Japan in 1976, has targeted different age groups, resulting in a large proportion of the current population being unvaccinated.Methods：Rubella cases reported in Tokyo from 2 January 2012 to 21 April 2013 were analysed. A clinical case had generalized maculopapular rash, fever and lymphadenopathy; a laboratory-confirmed case was a clinical case with a positive serology or polymerase chain reaction test for rubella. A descriptive analysis of cases by age, sex, vaccination history and other epidemiological information was conducted.Results：A total of 2382 cases were reported from all areas of Tokyo. Three-quarters were male ( n = 1823; 76.5%); the highest number of cases occurred among males aged 35–39 years and females aged 20–24 years. About a third of males (27%) and females (32%) reported never receiving rubella vaccination, with 68% and 56%, respectively, having an unknown vaccination status.Discussion：This outbreak reflects the changing, yet incomplete, immunization policies for rubella in Japan that may increase the risk of congenital rubella syndrome (CRS). To suppress the outbreak of rubella and prevent CRS cases, we recommend vaccination for the entire susceptible population.