A nebulizer for a fluid, particularly for medical aerosol treatment is proposed. To allow easier operation and confer improved operational reliability a sealed container holding the fluid is already arranged in the nebulizer when it is supplied and the nebulizer is constructed so that the container is opened inside the nebulizer before or during the first use of the nebulizer. For this purpose, a transportation lock is provided for the sealed container which, in the delivery state, is in engagement with the sealed container in a manner preventing the sealed container from moving axially in the nebulizer.