An outbreak of measles is ongoing in Geneva, Switzerland, since January 2011, in the context of a measles epidemic in neighbouring Rhône-Alpes, France. A total of 41 confirmed cases have been reported, the majority among young adults, many unaware of their non-immune status. There is no large clustering of cases and 14 cases were imported or linked to imported cases. Catch-up vaccination, especially among young adults, may be necessary to prevent further extension of this outbreak.