The bio-mechanical treatment of municipal solid waste (BMT) is an increasing option in Europe either as a pre-treatment before landfill or as a pre-treatment before combustion. The present work deals with the problem of assessment of significant data related to emissions to air from BMT. Reliable data are necessary for the development of: a) Life Cycle Assessment studies (LCA); b) verification of compliance with existing regulations; c) environmental impact studies assessment. In order to point out some lack of knowledge about BMTs, some results of a LCA study on MSW bio-stabilization treatment have been reported and analysed. Indeed, during the development of that LCA, some problems were found regarding the availability and the quality of emission data from MSW mechanical biological treatment. Concerning existing regulations, in Europe we can find countries with very different approaches. The studies of the environmental impact assessment of BMT are not still developed as options like incineration. The reason is that the impact of a BMT plant is considered low. On the contrary, it can be demonstrated that attention must be paid in case of not optimised technologies and large plants.