Let L be a second order uniformly elliptic operator, and consider the equation Lu = f under the boundary condition u = . We assume data f in generical subspaces of continuous functions D ω characterized by a given modulus of continuity ω(r), and show that the second order derivatives of the solution u belong to functional spaces Dω, characterized by a modulus of continuityω(r) expressed in terms of ω(r). Results are optimal. In some cases, as for Hölder spaces, Dω = D ω . In this case we say that full regularity occurs. In particular, full regularity occurs for the new class of functional spaces C ,λ α (Ω) which includes, as a particular case, the classical Hölder spaces C ,λ (Ω) = C ,λ (Ω). Few words, concerning the possibility of generalizations and applications to non-linear problems, are expended at the end of the introduction and also in the last section.