We investigate orthonormality-preserving, C * -conformal and conformal module mappings on full Hilbert C * -modules to obtain their general structure. Orthogonality-preserving bounded module maps T act as a multiplication by an element λ of the center of the multiplier algebra of the C * -algebra of coefficients combined with an isometric module operator as long as some polar decomposition conditions for the specific element λ are fulfilled inside that multiplier algebra. Generally, T always fulfills the equality T (x), T (y) = |λ| 2 x, y for any elements x, y of the Hilbert C * -module. At the contrary, C * -conformal and conformal bounded module maps are shown to be only the positive real multiples of isometric module operators.