This study compared the marginal fit of complete-arch fixed prostheses under simulated clinical conditions. Prostheses were made on casts constructed from three commonly used impression materials; polyether, polyvinyl siloxane (medium-viscosity and putty-wash), and reversible hydrocolloid. A maxillary dentoform with four abutment teeth was used as the master cast and six impressions were made with each material. Individual castings for each abutment were made on the stone casts. The abutment castings were luted together on the casts to provide a complete-arch fixed partial denture using a ticonium framework and acrylic resin. The marginal fit of the abutment castings was measured on the master cast before and after the prostheses were luted together. The polyether and both addition silicone impression materials were significantly more accurate than the reversible hydrocolloid in both situations. All of the single castings were clinically acceptable, but the luted restorations made from reversible hydrocolloids were not.