The critical considerations formulated by Tomatis et al. did not take into account all the experimental works and all the research on human pleura that from the Seventies on has unanimously indicated that asbestos fibre mesothelioma is caused by the ultrafine fibres class. These fibres that are so fine are not visible with light microscopy are mostly ultrashort, but they also include, in varying percentages, elements that are >5 microm long. The conclusions of Tomatis et al, which attribute mesothelioma to fibres of all lengths and diameters, are not confirmed in the literature. Today, mesothelioma prevention must consist of identifying and cutting down airborne ultrafine fibres, above all in urban environments. The techniques for doing so now exist and can be applied. The ultrafine class of asbestos, forgotten for decades, must be the principal target for prevention programs and must be widely monitored in work and daily life settings.