When dealing with inviscid flows, anisotropic mesh adaptation is commonly used to automatically get a high solution accuracy with a much lower computational effort than standard methods (uniform meshes, tai- lored meshes, h-refinement, . . . ). This gain increases with the level of anisotropy of the flow at hand. However, when viscous flows are involved, several problematics reduce the efficiency and the use of unstructured mesh adaptation. The first limitation concerns the adaptation of the surface mesh due to the presence of the bound- ary layer mesh. Projection to the true geometry may be either unfeasible or inefficient. Then, the creation of the boundary layer mesh itself becomes an even more complex problematic when an anisotropic surface is provided. Finally, the transition between the boundary layer and the adaptive mesh becomes of main concern, especially at transonic speeds where strong interactions between shocks and boundary layers exist. The scope of this paper is to introduce a unique mesh modification operator that is used at each adaptive step: from sur- face remeshing to boundary layer extrusion and volume mesh adaptation. For each case, the operator is based on a variety of choices for the cavity in order to insert or re-insert a surface or volume point in an unstructured or quasi-structured fashion.