The modified vaccinia virus Ankara (MVA) strain is a highly attenuated strain of vaccinia virus that has been demonstrated to be safe for humans. MVA is widely considered as the vaccinia virus strain of choice for clinical investigation because of its high safety profile. It also represents an excellent candidate for use as vector system in recombinant vaccine development for gene delivery or vaccination against infectious diseases or tumours, even in immunocompromised individuals. The use of MVA and recombinant MVA vectors must comply with various regulatory requirements, particularly relating to the assessment of potential risks for human health and the environment. The purpose of the present paper is to highlight some biological characteristics of MVA and MVA-based recombinant vectors and to discuss these from a biosafety point of view in the context of the European regulatory framework for genetically modified organisms with emphasis on the assessment of potential risks associated with environmental release.