Purpose: This study of 3-unit fixed partial dentures (FPDs) evaluated the long-term efficacy and determined the frequencies and causes of failures. Materials and Methods: A total of 134 FPDs made in an undergraduate university clinic for 98 patients were evaluated over a 20-year period. All patients were offered a supportive maintenance program. Failures of the FPDs were divided into irreversible (loss of FPDs) or reversible (FPDs intact after conservative treatment) complications and into biologic and technical/patient-related failures. Results: The overall survival rate was 73.1% after 20 years. There was a statistically significant difference (P = .036) between the survival rates in the mandible for the vital group (96.3%) versus the root canal-treated group (69.3%). Comparing the survival rate in the vital group for the restorations in the maxilla (70.2%) versus the mandible (96.3%), a statistically significant difference (P = .045) was found. The survival rate after 20 years for the 3-unit FPDs (73.1%) was significantly different from that of the FPDs with more than 3 units (61.5%) (P = .026). The main reason for failure was caries (38.1%). Conclusion: The survival of 3-unit FPDs over a 20-year period is favorable and should be compared with other single-tooth replacement treatment options. There is an indication that the occurrence of a reversible complication has a predictive value for an irreversible complication later on.