Like all nuclear power plants in Switzerland, the Paul Scherrer Institute in Villigen (PSI), Switzerland, has the duty to conduct an emergency exercise every year. The two monitoring authorities ENSI (Swiss Federal Nuclear Safety Inspectorate) and the BAG (Federal Office of Public Health – FOPH) use this exercise for their yearly audit of the emergency organization. The emergency organization of the Paul Scherrer Institute consists of the emergency staff, the fire brigade, the first aid station, the traffic- and the security platoon and the radiation safety, the latter consisting of the decontamination group, the radio analytics group and the measurement group (for radioactivity dispersion calculations). The framework is set up by the ENSI beforehand, based on a fixed cycle. For the emergency exercise of 2009 a plane crashing into the interim storage facility of the federal government (BZL) at PSI was assumed. This contribution describes the approach of the planning process, the performance and the evaluation of the exercise.