Fibroblasts can condense a hydrated collagen lattice to a tissue-like structure. The purpose of this study was to evaluate the effect of substrate adhesion on the contraction and mechanical properties of fibroblast populated collagen lattices. Bacteriological grade polystyrene (BGPS) plates and tissue culture polystyrene (TCPS) plates were used as substrates for incubation of fibroblast populated collagen lattices. Hydrophobicity of the polystyrene surfaces was measured by the static sessile contact angle method. Collagen lattice contraction was recorded for 2 weeks, after which the lattices were mechanically tested. The BGPS culture plate had a significantly larger contact angle and was more hydrophobic than the TCPS culture plate. Both hydrophobicity and peripheral detachment of the collagen gel significantly decreased the time lag before initiation of gel contraction and increased the strength of the fibroblast populated collagen lattices. Substrate adhesion affects the contractility and strength of cell seeded collagen gels. This information may be useful in developing tissue engineered tendons and ligaments.