This in vivo study examined the contribution of remaining coronal dentin and placement of a prefabricated or customized fiber post to the six-year survival of endodontically treated premolars. A sample of 345 patients provided 6 groups of 60 premolars in need of endodontic treatment. Groups were classified according to the number of remaining coronal walls before abutment build-up. Within each group, teeth were allocated to three subgroups: A) no post-retention; B) LP; C) ES (N=20). All teeth were protected with a crown. Cox regression analysis was applied to assess whether the amount of residual coronal dentin and the type of endocanalar retention had a significant influence on failure risk of the restored teeth.