When a polymer chain in solution interacts with an atomically smooth solid substrate, its conformational properties are strongly modified and deviate substantially from those of chains in bulk. In this work, the interplay of two competing transitions that affect. the conformations of polymer chains near an energetically attractive surface is studied by means of Monte Carlo simulations on a cubic lattice The transition from an extended to a compact conformation of a polymer chain near an attractive wall, as solubility deteriorates, exhibits characteristics akin to the "coil-to-globule" transition in bulk. An effective Theta-temperature is determined. Its role as the transition point is confirmed in a variety of ways. The nature of the coil-to-compact transition is not qualitatively different from that in the bulk. Adsorbed polymer chains may assume "globular" or "pancake" configurations depending on the competition among adsorption strength, cohesive energy, and entropy. In a very relevant range of conditions, the dependence of the adsorbate thickness on chain-length is intermediate between that of 3-d ("semidroplets") and 2-d ("pancake") objects. The focus of this study is on rather long polymer chains. Several crucial features of the transitions of the adsorbed chains are N-dependent and various aspects of the adsorption and "dissolution" process are manifested clearly only at the "long chain" limit. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2462-2476, 2009