The roughness of the substrate influences the adsorption phenomena in two different ways. At the bulk liquid-gas coexistence the first-order wetting temperature is decreased by the corrugation of the substrate, and the additional thin-thick first-order transition induced by the corrugation can appear independently of the order of the wetting transition. Thermodynamical analysis connects the existence of such transition with the curvature of the substrate. The mesoscopic mean-field analysis based on the effective interfacial Hamiltonian does not entirely confirm this macroscopic result. We analyse three kinds of substrate: piecewise convex, piecewise concave, and piecewise flat. The convex substrate does not exhibit the expected thin-thick transition. It is a consequence of the oversaturation of the vapour at the bulk liquid-gas coexistence over a convex substrate. (C) 2004 Elsevier B.V. All rights reserved.