Cells respond to geometrical cues, as well as to biochemical and mechanical stimuli. Recent progress in micro- and nano-technology has allowed researchers to create microbeads, micro-circular islands, and microposts, that can be used to examine the effect of geometrical cues on cellular behavior. Knowledge of changes in cell mechanics and morphology in response to geometric cues is important for understanding the basic behavior of cells during development and pathological processes. Most previous research in this area has focused on cell responses to two-dimensional planar or rectilinear structures. Very few studies have examined cell responses to three-dimensional curved structures because of the difficulty of fabricating such microstructures. Here we describe a novel method for the fabrication of convex and concave microstructures by use of a thin poly(dimethylsiloxane) (PDMS) membrane, SU-8 shadow mask, and negative air pressure without using any complicated silicon processes. We successfully fabricated concave and convex microstructures, with base diameters of 200-300 microm and depth (or height) of 50-150 microm (aspect ratios up to 1 : 0.5), and used these microstructures to study the responses of cultured L929 mouse fibroblast cells and human mesenchymal stem cells. These cells clearly sensed the three-dimensional microscale curvature and actively "escaped" from concave patterns, but not from those which were convex. Thus, it appears that microscale concave structures suppress cell adhesion and proliferation. We hypothesized that this might relate to deformation of the plasma membrane and subsequent opening of membrane channels. We anticipate that our system will be useful for various bio-MEMS (micro electro mechanical system) applications, including formation of uniformly-sized embryoid bodies, embryonic stem cell differentiation, and the fabrication of cell docking devices, microbioreactors, and microlenses as well as cell mechanics study.