In cost-effectiveness analysis and contemporary treatment planning strategies, the postponement of placement of cast crowns plays an important role. Extensive Amalgam Restorations (EAR), that involve the rebuilding of cusps and the provision of auxiliary retention, are thought to make this postponement possible. This study reports the long-term survival (100 months) of EAR in a randomized, controlled clinical trial. A total of 300 EAR were placed by 3 operators in molar teeth in which one or more cusps were reconstructed. Five different auxiliary retention methods were used for retention of these restorations. As the purpose of EAR is considered to be twofold (to restore a broken-down molar to acceptably function as an independent restoration and to create a substructure for subsequent crown construction), survival was assessed at different levels. The survival rate of EAR as an independent restoration was 88 ± 2%. The functional survival rate (as an independent restoration or as a substructure) was 92 ± 2%. The influence of experimental variables (retention method and operator) and background variables (tooth type, extension of EAR and age of patient) on the survival was analysed using Log Rank and Breslow tests. The analyses revealed that there were no statistically significant influences on the survival rates except for the variable ‘age of patient’ (p < 0.05). EAR was more prone to failure in the group of older patients than the group of younger ones.