The modified vaccinia virus Ankara (MVA) strain, which has been developed as a vaccine against smallpox, is since the nineties widely tested in clinical trials as recombinant vector for vaccination or gene therapy applications. Although MVA is renowned for its safety, several biosafety aspects need to be considered when performing the risk assessment of a recombinant MVA (rMVA). This paper presents the biosafety issues and the main lessons learned from the evaluation of the clinical trials with rMVA performed in Belgium. Factors such as the specific characteristics of the rMVA, the inserted foreign sequences/transgene, its ability for reconversion, recombination and dissemination in the population and the environment are the main points of attention. Measures to prevent or manage identified risks are also discussed.