3T3 fibroblasts were cultured on poly(dimethyl siloxane) line-shaped ridge/groove topography with a range of ridge widths (25-55 microm), ridge spacings (10-80 microm), and two ridge heights (15 and 21 microm). Three distinct regimes of attachment occurred, which were dependent on the ridge spacings used. Using the 21 microm height ridges, at the smallest spacings ( approximately 10-20 microm) cells were able to bridge between neighboring ridges without touching the groove floor below. At moderate spacings ( approximately 30-50 microm), 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 (> approximately 50 microm) 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 microm allowed ridge-groove connections also at 40 microm 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.