3T3 fibroblasts were cultured on poly(dimethyl siloxane) line-shaped ridge/groove topography with a range of ridge widths (25-55 mu m), ridge spacings (10-80 mu m), and two ridge heights (15 and 21 mu m). Three distinct regimes of attachment occurred, which were dependent on the ridge spacings used. Using the 21 mu m height ridges, at the smallest spacings (similar to 10-20/mu m) cells were able to bridge between neighboring ridges without touching the groove floor below. At moderate spacings (similar to 30-50 mu m), cells were confined to a single ridge or groove only and aligned to the pattern at an increasing degree as the ridge width narrowed. The largest spacings (>similar to 50 mu m) allowed cells to connect between a ridge and a groove, and the connection occurred most frequently at angles nearly perpendicular to the pattern. Reducing the ridge height to 15 mu m allowed ridge-groove connections also at 40 mu m spacings but had no effect on bridging or alignment. It was proposed that both a critical length and a critical angle (slope) exist for any cell protuberance that connects between a ridge-ridge or ridge-groove. These results build on previous studies by using a single cell type and focusing quantitatively on the regimes permitting different modes of spreading. In addition, particular focus on the ridge-groove connections has allowed more comprehensive quantification of the incident angles and morphologies of cells as they connect between a ridge and a groove.